Method and apparatus for watermark signal embedding and detection using two-dimensional reference pattern

Abstract

The present invention relates to a method and apparatus for inserting and detecting a watermark to conceal information in digital media, and more specifically, to a method for reliably detecting a watermark even when there is distortion due to projection using a two-dimensional reference pattern, and to an apparatus for executing such a method. A method for inserting a watermark signal according to one embodiment of the present invention comprises the steps of receiving a target image to which a watermark is to be inserted, generating a watermark pattern to be inserted into the target image, generating a two-dimensional reference pattern, determining the position of the two-dimensional reference pattern relative to the watermark pattern, inserting the watermark pattern and the two-dimensional reference pattern into the target image, and outputting an image with the watermark inserted therein, wherein the two-dimensional reference pattern may be characterized as being robust against projection distortion.

Description

Technology Field

[0001] The present invention relates to a method and apparatus for inserting and detecting a watermark to conceal information in digital media, and more specifically, to a method and apparatus for implementing such a method that can reliably detect a watermark even when there is distortion due to perspective using a two-dimensional reference pattern. Background Technology

[0002] Recently, almost all tasks and services in daily life, such as office work, payment services, certificate issuance, banking, e-commerce, and the provision of cultural media, are being carried out through online and computerized environments. In such online and computerized environments, digital media serves as the subject of information creation, viewing, storage, editing, and transmission. In this context, digital media can refer to various forms of digital information, including images, text, and multimedia, such as digital documents, images, audio, video, and three-dimensional data.

[0003] However, due to the nature of digital information, such digital media can be easily copied or transmitted without loss of information, making them highly vulnerable to leakage through illegal activities. Therefore, to provide a healthy digital media usage environment, protective measures—namely, security systems—that can prevent digital media from being compromised by illegal activities are essential. For example, digital media can be protected through encryption and decryption systems, watermark or fingerprinting systems, and screen capture prevention systems.

[0004] One such method is digital watermarking. Many commonly used digital watermarking methods involve a process of embedding specific additional information by applying a machine-readable manipulation at a temporally or spatially defined location on digital media. The embedded additional information can be detected by analyzing the watermarked digital media using a device or software configured to interpret the manipulation.

[0005] The above additional information may be information indicating ownership of the digital media, or information indicating that copying or viewing is restricted. In particular, such additional information may be embedded in the digital media in a form that is effectively invisible by applying operations that are imperceptible to the viewer of the digital media but readable by a machine.

[0006] Furthermore, recently, forensic watermarking methods have been used to insert traceability information as supplementary data into leaked videos using digital watermarking. Distributing digital media with recipient information embedded within it can help identify individuals who use the media in unauthorized ways or participate in the illegal leakage of digital media.

[0007] One of the leading methods for inserting digital watermarks has conventionally utilized the frequency domain. This prior art involves applying a transform function, such as the Fourier transform or cosine transform, to convert digital media in the form of general information into frequency information, inserting a watermark into the resulting frequency information, and then restoring it to its original form by performing an inverse transform.

[0008] Another promising method for inserting digital watermarks is the conventional method of utilizing superposition operations, such as pattern overlay or alpha blending, in the spatial domain. This prior art includes forming a digital pattern according to a predetermined rule and / or encryption method, and overlaying the pattern in the spatial domain in a visible or invisible form by applying a predetermined transparency or using various mathematical techniques.

[0009] Although the fundamental principles of the aforementioned prior art are widely known, deriving specific implementation methods remains a constant challenge, due to the requirement that sufficient robustness must be guaranteed. It cannot be asserted that digital media is distributed only in the form it was in at the time the watermark was inserted, and digital media may be altered or damaged due to technical reasons or intentional manipulation during the distribution process and / or illegal leakage. In particular, acts of damaging or distorting information to evade tracking by the aforementioned forensic watermark—so-called "attacks on watermarks"—can occur at any time.

[0010] In particular, in environments where digital media containing watermarks cannot be utilized for detection in their original form—for instance, when acquired by re-photographing the form of a displayed screen or printed media—perspective distortion occurs. Perspective distortion can be caused by various factors, such as camera lens characteristics, shooting angle, and distance; this leads to a deformation of the geometric shape of the watermarked area, making watermark detection difficult. Conventionally, to address this perspective distortion, methods such as estimating and correcting geometric distortion by analyzing frequency correlations of the watermark pattern or detecting and correcting feature points within the image were used. However, these methods had limitations in correction when severe perspective distortion occurred. Furthermore, when the watermark itself was damaged or incompletely acquired, it was difficult to obtain the information necessary for correction, resulting in a significant decrease in the detection rate.

[0011] Therefore, new technical means are required to insert and detect watermarks in a manner robust to such projection distortion. The problem to be solved

[0012] The present invention aims to provide a new method for detecting a watermark embedded in digital media robustly against geometric deformations including projection distortion, and an apparatus for implementing such a method.

[0013] Specifically, the purpose is to provide a watermark insertion and detection method that accurately estimates and corrects projection transformation information using a two-dimensional reference pattern so as to reliably detect a watermark even when there is projection distortion caused by screen shooting or capturing, and an apparatus for executing such a method. means of solving the problem

[0014] A method for inserting a watermark signal according to an embodiment of the present invention for solving the aforementioned technical problem comprises the steps of receiving a target image to which a watermark is to be inserted, generating a watermark pattern to be inserted into the target image, generating a two-dimensional reference pattern, determining the position of the two-dimensional reference pattern relative to the watermark pattern, inserting the watermark pattern and the two-dimensional reference pattern into the target image, and outputting an image with the watermark inserted therein, wherein the two-dimensional reference pattern may be characterized as being robust against perspective distortion.

[0015] The above two-dimensional reference pattern may be characterized as being one of an ArUco marker, an AprilTag, a WhyCon marker, a ChArUco marker, a QR code, and a DataMatrix.

[0016] The above two-dimensional reference pattern may be characterized by being placed in the corner area of ​​the above watermark pattern.

[0017] The above two-dimensional reference pattern may include a plurality of two-dimensional reference patterns, and the plurality of two-dimensional reference patterns may be characterized by having the same key value or different key values.

[0018] The above plurality of two-dimensional reference patterns may be characterized by having different key values, and the different key values ​​may be used to indicate the directionality of the watermark pattern.

[0019] The above two-dimensional reference pattern may be characterized by being arranged in a manner that minimizes interference with the target image and the watermark pattern.

[0020] The step of determining the position of the above-described two-dimensional reference pattern may be characterized by determining the position of the above-described two-dimensional reference pattern to minimize interference by avoiding a noise-generating area during printing, and the above-described two-dimensional reference pattern being placed at the said position.

[0021] The above method may further include the step of setting the transparency of the two-dimensional reference pattern, and the watermark pattern and the two-dimensional reference pattern may be characterized by being arranged to spatially overlap each other.

[0022] The above watermark pattern and the above two-dimensional reference pattern may be characterized by being arranged so as not to spatially overlap each other.

[0023] The above two-dimensional reference pattern may be characterized by being inserted into the target image in the frequency domain.

[0024] The above two-dimensional reference pattern may be characterized by being inserted into the target image in a spatial region.

[0025] The above two-dimensional reference pattern may be characterized by being configured to represent at least a portion of the information represented by the watermark pattern by encoding it.

[0026] The step of generating the watermark pattern may be characterized by generating a watermark pattern that is displayed as at least one two-dimensional reference pattern, and the step of generating the two-dimensional reference pattern may be configured to generate a two-dimensional reference pattern that constitutes at least a part of the watermark by the watermark pattern.

[0027] The image to be inserted is characterized by being unfolded in a three-dimensional space, the watermark pattern is configured to be recognized by being displayed on at least one surface in the three-dimensional space, and the two-dimensional reference pattern may be characterized by being used to specify at least one of the direction, order, and content of the watermark detected from the at least one surface in the three-dimensional space.

[0028] A watermark detection method according to an embodiment of the present invention for solving the aforementioned technical problem may include the steps of receiving an image to be detected as a watermark; detecting a two-dimensional reference pattern in the image to be detected; calculating perspective distortion information based on at least one of the position and shape of the detected two-dimensional reference pattern; correcting geometric distortion of the image to be detected based on the calculated perspective distortion information; and detecting a watermark from the image to be detected in which geometric distortion has been corrected.

[0029] The step of detecting the above two-dimensional reference pattern may be characterized by detecting a two-dimensional pattern among an ArUco marker, an AprilTag, a WhyCon marker, a ChArUco marker, a QR code, and a DataMatrix.

[0030] The step of calculating the projection distortion information may be characterized by calculating the projection distortion information by synthesizing the information obtained from the plurality of two-dimensional reference patterns when a plurality of two-dimensional reference patterns are detected.

[0031] A watermark insertion device according to an embodiment of the present invention for solving the aforementioned technical problem comprises a processor, a memory connected to the processor, an image input unit for receiving a target image to which a watermark is to be inserted, a watermark pattern generation unit for generating a watermark pattern to be inserted into the target image, a two-dimensional reference pattern generation unit for generating a two-dimensional reference pattern, a pattern position determination unit for determining the position of the two-dimensional reference pattern relative to the watermark pattern, a watermark insertion unit for inserting the watermark pattern and the two-dimensional reference pattern into the target image, and an output unit for outputting the image with the watermark inserted therein, wherein the two-dimensional reference pattern may be characterized as being robust against perspective distortion.

[0032] A watermark detection device according to an embodiment of the present invention for solving the aforementioned technical problem may include a processor, a memory connected to the processor, an image input unit for receiving an image to be detected as a watermark, a pattern detection unit for detecting a two-dimensional reference pattern in the image to be detected, a distortion calculation unit for calculating perspective distortion information based on at least one of the position and shape of the detected two-dimensional reference pattern, a distortion correction unit for correcting geometric distortion of the image to be detected based on the calculated perspective distortion information, and a watermark detection unit for detecting a watermark from the image to be detected in which geometric distortion has been corrected.

[0033] A recording medium according to an embodiment of the present invention for solving the aforementioned technical problem may have an information recording area, wherein image information having a watermark pattern and a two-dimensional reference pattern robust against perspective distortion may be recorded in the information recording area, and the two-dimensional reference pattern may be characterized by having a structure capable of estimating transformation information regarding the perspective distortion applied to the image information. Effects of the invention

[0034] According to the present invention, a watermark detection method and apparatus robust to projection distortion can be provided by inserting a two-dimensional reference pattern together with a watermark.

[0035] According to one embodiment of the present invention, by accurately acquiring projection transformation information through a two-dimensional reference pattern accompanying the watermark and restoring the original form of the watermark, there is an effect of stably detecting the watermark even when complex geometric distortion occurs.

[0036] According to one embodiment of the present invention, the two-dimensional reference pattern itself can be utilized for information storage purposes, and by encoding part or all of the watermark message into the two-dimensional reference pattern, there is an advantage of increasing the detection success rate or enabling the transmission of additional information.

[0037] According to one embodiment of the present invention, security can be enhanced by utilizing a specific pattern of a two-dimensional reference pattern as a key value, and detection performance can be improved while minimizing visual quality degradation by optimizing the pattern insertion position or the shape of the inserted pattern according to the characteristics of the image to be inserted. Brief explanation of the drawing

[0038] FIG. 1 is an exemplary diagram of the combination of a watermark pattern and a two-dimensional reference pattern according to an embodiment of the present invention. FIG. 2 is a conceptual diagram of a case in which a watermark pattern according to an embodiment of the present invention is obtained in a projected state, FIG. 3 is another exemplary illustration of the combination of a watermark pattern and a two-dimensional reference pattern according to one embodiment of the present invention. FIG. 4 is a conceptual diagram of the possibility of overlapping placement of watermarks according to an embodiment of the present invention, FIG. 5 is an exemplary diagram showing a shape change according to a prior configuration difference of a reference pattern according to an embodiment of the present invention. FIG. 6 is an example of a watermark composed of a two-dimensional reference pattern according to an embodiment of the present invention. FIG. 7 is an exemplary diagram of a watermark implemented to be placed in a three-dimensional space and capable of being captured and decoded according to an embodiment of the present invention. FIG. 8 is a flowchart illustrating a watermark insertion method including a two-dimensional reference pattern according to an embodiment of the present invention, FIG. 9 is a flowchart illustrating a method for detecting a watermark including a two-dimensional reference pattern according to an embodiment of the present invention, FIG. 10 is a block diagram showing the configuration of a watermark insertion device according to an embodiment of the present invention, and FIG. 11 is a block diagram showing the configuration of a watermark detection device according to one embodiment of the present invention. Specific details for implementing the invention

[0039] The present invention is capable of various modifications and may have various embodiments, and specific embodiments are illustrated in the drawings and described in detail. However, this is not intended to limit the invention to specific embodiments, and it should be understood that the invention includes all modifications, equivalents, and substitutions that fall within the spirit and scope of the invention.

[0040] Terms such as "first," "second," etc., may be used to describe various components, but said components should not be limited by said terms. These terms are used solely for the purpose of distinguishing one component from another. For example, without departing from the scope of the present invention, the first component may be named the second component, and similarly, the second component may be named the first component. The term "and / or" includes a combination of multiple related described items or any of the multiple related described items, and is non-exclusive unless otherwise indicated. Where items are listed in this specification, they are merely illustrative descriptions intended to facilitate the explanation of the inventive spirit and possible embodiments set forth in this specification, and are therefore not intended to limit the scope of the embodiments of the present invention.

[0041] In this specification, "A or B" may mean "only A," "only B," or "both A and B." Alternatively, in this specification, "A or B" may be interpreted as "A and / or B." For example, in this specification, "A, B or C" may mean "only A," "only B," "only C," or "any combination of A, B and C."

[0042] A slash ( / ) or a comma used in this specification may mean "and / or." For example, "A / B" may mean "A and / or B." Accordingly, "A / B" may mean "only A," "only B," or "both A and B." For example, "A, B, C" may mean "A, B or C."

[0043] In this specification, "at least one of A and B" may mean "only A," "only B," or "both A and B." Additionally, in this specification, the expressions "at least one of A or B" or "at least one of A and / or B" may be interpreted as synonymous with "at least one of A and B."

[0044] Additionally, in this specification, "at least one of A, B and C" may mean "only A," "only B," "only C," or "any combination of A, B and C." Also, "at least one of A, B or C" or "at least one of A, B and / or C" may mean "at least one of A, B and C."

[0045] When it is stated that one component is "connected" or "connected" to another component, it should be understood that while it may be directly connected or connected to that other component, there may also be other components in between. On the other hand, when it is stated that one component is "directly connected" or "directly connected" to another component, it should be understood that there are no other components in between.

[0046] The terms used herein are merely for describing specific embodiments and are not intended to limit the invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In this specification, terms such as “comprising” or “having” are intended to indicate the presence of the features, numbers, steps, actions, components, parts, or combinations thereof described in the specification, and should be understood as not precluding the existence or addition of one or more other features, numbers, steps, actions, components, parts, or combinations thereof.

[0047] Unless otherwise defined, all terms used herein, including technical or scientific terms, are used with the same meaning as generally understood by those skilled in the art to which the present invention pertains. Terms such as those defined in commonly used dictionaries should be interpreted as having a meaning consistent with their meaning in the context of the relevant technology, and should not be interpreted in an ideal or overly formal sense unless explicitly defined in this specification.

[0048] In describing the invention in this specification, embodiments may be described or illustrated in terms of the described functions or unit blocks that perform the functions. The blocks may be expressed in this specification as one or more devices, units, modules, parts, etc. The blocks may be implemented in hardware by a method of implementing one or more logic gates, integrated circuits, processors, controllers, memory, electronic components, or information processing hardware, which are not limited thereto. Alternatively, the blocks may be implemented in software by a method of implementing application software, operating system software, firmware, or information processing software, which are not limited thereto. A single block may be implemented by being separated into multiple blocks that perform the same function, or conversely, a single block may be implemented to simultaneously perform the functions of multiple blocks. The blocks may also be implemented by being physically separated or combined according to any criteria. The blocks may be implemented to operate in an environment where their physical locations are not specified and they are spaced apart from each other by a communication network, the Internet, a cloud service, or a communication method not limited thereto. Since all of the above-mentioned methods of implementation fall within the scope of various embodiments that a person skilled in the art familiar with the field of information and communication technology can adopt to realize the same technical concept, any detailed methods of implementation should be interpreted as being included within the scope of the technical concept of the invention as set forth in this specification.

[0049] Hereinafter, preferred embodiments of the present invention will be described in more detail with reference to the attached drawings. In describing the present invention, to facilitate overall understanding, the same reference numerals are used for identical components in the drawings, and redundant descriptions of identical components are omitted. Furthermore, it is assumed that multiple embodiments are not mutually exclusive and that some embodiments may be combined with one or more other embodiments to form new embodiments.

[0051] Watermark combination of two-dimensional reference patterns

[0052] The core of the watermark insertion and detection method according to the present invention is to implement a watermark system robust to projection distortion by combining a two-dimensional reference pattern with existing watermark technology. The two-dimensional reference pattern according to the present invention can possess the characteristic of accurately identifying the shape and location of the pattern even when distortion occurs due to projection transformation, thereby enabling accurate estimation and correction of geometric distortion in the area where the watermark is inserted.

[0053] In a preferred embodiment of the present invention, the two-dimensional reference pattern may be configured to satisfy the following technical requirements. According to one embodiment, it may be configured to accurately detect the pattern even if geometric distortion occurs due to projection transformation. According to one embodiment, it may be configured to accurately derive a perspective transformation matrix through the detection of the pattern. According to one embodiment, it may be configured so that the structure of the pattern is simple and clear, making detection easy, and so that it can be stably recognized even under various environmental conditions.

[0054] In the present invention, the two-dimensional reference pattern is not limited by details other than the technical concept thereof. That is, any representational construct that provides a function for recognizing and correcting distortion caused by projection transformation may be considered as a two-dimensional reference pattern according to the present invention. In particular, a two-dimensional barcode or identification pattern having any shape may be used as the two-dimensional reference pattern. Examples of the two-dimensional barcode or identification pattern may include an ArUco marker, an AprilTag, a WhyCon marker, a ChArUco marker, a QR code, a DataMatrix, and various other two-dimensional pattern formation methods that are conventionally known or can be newly constructed.

[0055] In this specification, the configuration of the invention is described using the Arco marker as a representative example of the two-dimensional reference pattern for easy understanding of the invention. However, as described above, the present invention can be implemented by various two-dimensional patterns, and it will be obvious to those skilled in the art that the embodiments of the present invention are not limited by the contents of the disclosure for explaining the present invention.

[0056] The above-described Arco Marker corresponds to a two-dimensional binary code pattern that corrects perspective distortion and enables accurate spatial recognition in computer vision systems. The basic structure of the Arco Marker is square-shaped and consists of a black border and an internal binary matrix. The outer border of the marker is designed for rapid detection, allowing the marker to be quickly identified within an image. The internal matrix represents the marker's unique identifier as a binary code, providing error detection and correction functions. The reason the Arco Marker is particularly suitable as a two-dimensional reference pattern for the present invention lies in its robustness against projection distortion and ease of application. The Arco Marker was originally developed for applications in the fields of Augmented Reality (AR) and Virtual Reality (VR), and as such, it possesses robust projection distortion correction performance that allows for stable recognition even at various shooting angles and distances. Furthermore, it has the advantage of being easy to implement as it is supported by widely known computer vision libraries such as OpenCV.

[0057] However, these advantages disclosed in this specification represent desirable technical characteristics that a two-dimensional pattern may possess that can be used in the implementation of the present invention, and should be understood as indicating that various two-dimensional patterns having the same or similar characteristics may be used, and do not imply that the present invention is technically dependent on the form of a specific pattern or limited by some specific type of pattern.

[0058] FIG. 1 is an exemplary diagram illustrating the combination of a watermark pattern and a two-dimensional reference pattern according to an embodiment of the present invention. FIG. 1 illustrates an exemplary form in which an Arco marker, as a two-dimensional reference pattern according to an embodiment of the present invention, is combined with a watermark pattern. Referring to FIG. 1, Arco markers (121, 122, 123, 124) are respectively placed at the four corners of a rectangular watermark pattern (100). In this configuration, the Arco markers (121, 122, 123, 124) serve as reference points that can accurately identify the spatial position and direction of the watermark pattern (100).

[0059] FIG. 2 is a conceptual diagram of a case in which a watermark pattern according to an embodiment of the present invention is obtained in a projected state. FIG. 2 illustrates a situation in which an image with the watermark inserted according to FIG. 1 is displayed on a wall and captured by a camera. Referring to FIG. 2, the watermark-inserted image appearing in the captured image (200) has the Arco Markers (221, 222, 223, 224) deformed along with the watermark pattern (210) due to projection distortion. At this time, due to the structural characteristics of each Arco Marker, their position and shape can be accurately identified even in a deformed state, and through this, the projection transformation information applied to the watermark pattern (210) can be accurately estimated. Through the Arco Markers (221, 222, 223, 224), the boundary points and distortion shape of the watermark can be identified, and since it is possible to determine how markers of the same size are deformed and displayed at each point, the warping of the watermark pattern (210) becomes easier.

[0061] Various combination methods of two-dimensional reference patterns

[0062] According to one embodiment of the present invention, two-dimensional reference patterns placed at each corner of a watermark pattern may have the same key value or different key values. If they have the same key value, there is an advantage in improving the detectability of the pattern. On the other hand, if they have different key values, they can be utilized to determine the directionality of the watermark pattern. For example, if a specific key value is assigned to a two-dimensional reference pattern located at the top-left corner, the original direction of the watermark pattern can be accurately identified and corrected even when the shooting direction is significantly rotated.

[0063] According to another embodiment of the present invention, each two-dimensional reference pattern may be limited to a pattern having a specific representation value. This specific representation value may be used for various purposes, such as being used as an identification key value for a watermark, distinguishing information types of different watermarks, or being utilized as an error correction code for watermark information. For example, in the case of an Arco marker, an additional security layer may be provided to the watermark system by selectively using only specific ID values ​​(e.g., #7, 22, 35, 47, etc.) from a specific dictionary.

[0064] FIG. 3 is another example of the combination of a watermark pattern and a two-dimensional reference pattern according to an embodiment of the present invention. FIG. 3 illustrates a case where at least one two-dimensional reference pattern placed at the corners of the watermark pattern has different representation values. Referring to FIG. 3, the aruco markers (321, 322, 323, 324) located at the four corners of the watermark pattern (310) each have different ID values. Specifically, the aruco marker (321) at the top left has an ID value of '7', the aruco marker (322) at the top right has an ID value of '22', the aruco marker (323) at the bottom left has an ID value of '35', and the aruco marker (324) at the bottom right has an ID value of '47'. By using aruco markers with different ID values ​​in this way, the direction of the watermark pattern (310) can be clearly identified, and the combination of these ID values ​​can also be utilized as an authentication key for the watermark system.

[0065] According to another embodiment of the present invention, a two-dimensional reference pattern and a watermark pattern may or may not overlap each other. FIG. 4 is a conceptual diagram of the possibility of overlapping placement of watermarks according to an embodiment of the present invention. FIG. 4(a) and FIG. 4(b) respectively illustrate an exemplary placement method according to different overlapping characteristics. Referring to FIG. 4(a), the watermark pattern (410) and the two-dimensional reference pattern, the Arco Marker (421), are placed separately without overlapping each other. On the other hand, referring to FIG. 4(b), the watermark pattern (450) overlaps with the two-dimensional reference pattern, the Arco Marker (461). The non-overlapping placement has the advantage of increasing the recognition rate of each pattern, while the overlapping placement has the advantage of increasing spatial efficiency.

[0066] In various embodiments of the present invention, a two-dimensional reference pattern may be implemented in different forms by various configuration methods, even if it has the same specifications. For example, in the case of an Arco marker, various shapes corresponding to different values ​​may be generated depending on the difference in the number of pixels and the dictionary. By allowing the watermark insertion system and the detection system to share information regarding these various implementation methods, the watermark detection capability can be increased or the information transmission capability can be enhanced.

[0067] FIG. 5 is an exemplary diagram illustrating a change in shape according to a difference in the prior configuration of a reference pattern according to an embodiment of the present invention. Referring to FIG. 5, three different Arco marker implementations (510, 520, 530) representing the same ID value '22' are presented as examples. The first Arco marker (510) uses a 4x4 bit dictionary "DICT_4X4", the second Arco marker (520) uses a 5x5 bit dictionary "DICT_5X5", and the third Arco marker (530) uses a 6x6 bit dictionary "DICT_6X6". As shown in FIG. 5, even with the same ID value, it can be implemented in different sizes and shapes depending on the configuration method of the reference pattern, and this diversity increases the flexibility of the watermark system and enables implementations optimized for specific application environments.

[0068] According to one embodiment of the present invention, the transparency and visibility of a two-dimensional reference pattern may be set identically to or independently of the watermark pattern. According to one embodiment of the present invention, both the watermark pattern and the two-dimensional reference pattern may be formed in a visible form. However, according to other embodiments of the present invention, the watermark pattern may be invisible while only the two-dimensional reference pattern is visible, the watermark pattern may be visible while the two-dimensional reference pattern is invisibly embedded, or both the watermark pattern and the two-dimensional reference pattern may be formed invisibly. The invisibility may refer to a level of invisibility equivalent to that of an "invisible" watermark commonly referred to in the field of digital watermarks through the control of transparency, adaptation to the data to be inserted, and other methods, and it is evident that this does not refer to a level that is completely transparent or completely visually imperceptible.

[0069] According to another embodiment of the present invention, part or all of a watermark can be constructed using only two-dimensional reference patterns. In this case, information can be hidden by arranging multiple two-dimensional reference patterns having different key values. FIG. 6 illustrates an example of a watermark composed of two-dimensional reference patterns according to an embodiment of the present invention. Referring to FIG. 6, an example is illustrated in which multiple Arco markers are arranged in a grid shape to form a watermark pattern (600) itself. At this time, each Arco marker may have a different ID value, and a sequence of these ID values ​​may be configured to encode a watermark message. This configuration simplifies the implementation of the system because the two-dimensional reference pattern itself can perform the role of conveying the watermark message without the need to maintain the watermark pattern and the two-dimensional reference pattern separately. Furthermore, it should be understood that watermark information composed solely of the two-dimensional reference patterns can be inserted as a watermark in various ways that are not limited to examples, such as being visible or invisible, applied by a certain transparency or blending method, or merged and / or inserted in the frequency domain, as described in the various embodiments above.

[0070] According to one embodiment of the present invention, the placement position of the two-dimensional reference pattern is not limited to the corners of the watermark pattern as previously described, but can be designated at any location on the image or watermark pattern to be inserted. Depending on the embodiment, a method may be adopted in which the position of the two-dimensional reference pattern adaptively changes according to the characteristics of the image or watermark pattern to be inserted.

[0071] According to one embodiment of the present invention, the placement location of a two-dimensional reference pattern can be determined by considering the accuracy of pattern recognition. For example, in the case of an image with a watermark inserted in a printed material, if the two-dimensional reference pattern is placed in an area prone to generating high-frequency noise or moiré patterns, such as in halftone printing, the pattern recognition rate may decrease. Therefore, it is desirable to place the two-dimensional reference pattern while avoiding such areas. This positioning can be performed manually or adaptively through image analysis.

[0072] According to one embodiment of the present invention, a method for addressing low-frequency noise that may occur when inserting a two-dimensional reference pattern may be applied. When inserting a two-dimensional reference pattern, such as a 2D barcode like an Arco marker, noise may occur in the low-frequency region due to the high-contrast characteristics of the boundary and internal pattern of the pattern. Since such noise can cause interference with the watermark signal in the frequency domain, the present invention provides a method to minimize this. According to various embodiments of the present invention, the following techniques may be applied to reduce low-frequency noise when inserting a two-dimensional reference pattern. For example, the occurrence of low-frequency noise can be suppressed by applying a gradual gradient to the boundary of the two-dimensional reference pattern to mitigate high-contrast boundaries. As another example, interference with the watermark signal in the frequency domain can be minimized by optimizing the size and position of the two-dimensional reference pattern. As yet another example, interference can be prevented by excluding specific frequency bands affected by the two-dimensional reference pattern in the frequency domain during the watermark insertion process or by setting a low weight for those bands.

[0073] According to another embodiment of the present invention, by utilizing the projection distortion correction characteristics of a two-dimensional reference pattern, a watermark placed in a three-dimensional space rather than a single plane can be generated and detected. FIG. 7 illustrates an example of a watermark implemented to be placed in a three-dimensional space and capable of being captured and decoded according to an embodiment of the present invention. Referring to FIG. 7, a watermark pattern and a two-dimensional reference pattern are inserted across three faces (710, 720, 730) of a three-dimensional object (700). The two-dimensional reference patterns (715, 725, 735) placed on each face enable accurate identification of the spatial position and orientation of the corresponding face, and can be configured to be utilized to accurately detect the watermark patterns (712, 722, 732) inserted on each face. As described above, the watermark placed in a three-dimensional space can be utilized for augmented reality applications in actual physical environments or for three-dimensional product authentication.

[0075] Method for inserting a watermark containing a reference pattern

[0076] FIG. 8 is a flowchart illustrating a watermark insertion method including a two-dimensional reference pattern according to an embodiment of the present invention. Referring to FIG. 8, the watermark insertion method of the present invention may include the following steps.

[0077] First, a target image to be watermarked can be received (S810). The target image may be various forms of digital media, such as digital images, video frames, or documents. Next, a watermark pattern to be inserted can be generated (S820). The watermark pattern may be in the form of encoded data for various purposes, such as copyright information, ownership information, or traceability information. Subsequently, a two-dimensional reference pattern to be inserted can be generated (S830). As previously described, the two-dimensional reference pattern may be generated by selecting from various types of patterns, such as Arco Markers, and an appropriate size, number of bits, and dictionary suitable for the application environment may be determined.

[0078] Optionally, the location of the two-dimensional reference pattern can be determined by considering the characteristics of the target image and / or watermark pattern (S840). In this step, an optimal location can be determined to maximize the pattern recognition rate and minimize the degradation of visual quality. Also optionally, the transparency and visibility of the two-dimensional reference pattern can be set (S850). In this step, an appropriate level of transparency suitable for the application environment can be determined, and a transparency setting that is identical to or independent of the watermark pattern is possible.

[0079] Then, a watermark pattern and a two-dimensional reference pattern can be inserted into the target image (S860). The insertion method at this step may be any of the frequency domain-based insertion method, pattern overlay method, or various other watermark insertion methods described in the background art. Additionally, as described above, the two-dimensional reference pattern may be inserted in the same way as the watermark pattern or in a different way, and may be inserted simultaneously or sequentially. Finally, the image with the watermark containing the two-dimensional reference pattern inserted can be output (S870). The output image may be stored in digital form, printed, displayed, or transmitted over a network.

[0080] According to a preferred embodiment of the present invention, a watermark pattern may be inserted in the frequency domain, and a two-dimensional reference pattern may be inserted in an overlay manner in the spatial domain. This combination has the advantage of utilizing both the invisibility and robustness of the watermark and the accurate detection characteristics of the two-dimensional reference pattern. According to another embodiment of the present invention, both the watermark pattern and the two-dimensional reference pattern may be inserted in the frequency domain. In this case, it is desirable to use different frequency bands so that the two patterns do not interfere with each other in the frequency domain. According to yet another embodiment of the present invention, both the watermark pattern and the two-dimensional reference pattern may be inserted in an overlay manner in the spatial domain. In this case, transparency and positioning that consider both the visual quality and detection performance of the two patterns are important.

[0082] Watermark detection method through correction of projection distortion

[0083] FIG. 9 is a flowchart illustrating a method for detecting a watermark including a two-dimensional reference pattern according to an embodiment of the present invention. Referring to FIG. 9, the watermark detection method of the present invention may include the following steps.

[0084] First, a target image for detection can be input by capturing or acquiring an image with a watermark inserted (S910). The target image for detection can be acquired through a digital camera, a smartphone, or other image acquisition device, and it is obvious that projection distortion may occur during this process. Next, a two-dimensional reference pattern can be detected in the input image (S920). According to a preferred embodiment of the present invention, an Arco marker within the image can be identified using an Arco marker detection algorithm. In this process, relevant functions of a computer vision library such as OpenCV can be utilized.

[0085] As described above, when a two-dimensional reference pattern is detected, projection transformation information can be estimated by analyzing the location and shape of the detected pattern (S930). Specifically, in the step of estimating the projection transformation information (S930), a homography matrix can be calculated using the corner coordinates of the detected two-dimensional reference pattern. The homography matrix may represent a mathematical expression of the projection transformation relationship from the distorted image plane to the original image plane. Next, the geometric distortion of the watermark-inserted area can be corrected using the estimated projection transformation information (S940). For example, in this process, the distorted area can be inversely transformed back to its original form using the previously calculated homography matrix. At this time, the inverse transformation can be implemented through an image geometric transformation algorithm such as the "warpPerspective" function of OpenCV.

[0086] After geometric distortion is corrected, a watermark can be detected in the corrected image (S950). In this step, a detection algorithm corresponding to the original watermark insertion method may be applied. For example, in the case of a watermark inserted in the frequency domain, the watermark may be detected by analyzing the corresponding frequency components after frequency conversion, and in the case of a watermark inserted using a pattern overlay method, the watermark may be detected through a pattern matching technique. Additionally, various other watermark detection methods not exemplified in the specification of the present invention may be implemented and practiced as part of the present invention.

[0087] Based on the result of detecting the watermark, the detected watermark message can be interpreted and processed (S960). Depending on the embodiment, the watermark message can be verified or additional information processing can be performed by utilizing key values ​​or additional information stored in a two-dimensional reference pattern as needed.

[0088] Finally, the detection result is output (S970). The output result may include the content of the watermark message, whether detection was successful, and other related information.

[0089] According to a preferred embodiment of the present invention, when a plurality of two-dimensional reference patterns are detected, more accurate projection transformation information can be estimated by utilizing all of them. For example, when all Arco markers placed at the four corners of a watermark pattern are detected, a homography matrix can be calculated based on a total of 16 corresponding points by utilizing all four corner points of each marker. This utilization of multiple patterns can significantly improve the accuracy and stability of projection transformation estimation.

[0090] According to another embodiment of the present invention, watermark detection is possible even when only some two-dimensional reference patterns are detected. For example, even when only three of the four Arco markers are detected, the position of the fourth marker can be estimated and overall projection transformation information derived by analyzing the positional relationship of the three detected markers. Robustness in such partial detection situations is a very important factor in actual application environments.

[0091] According to another embodiment of the present invention, information encoded in the two-dimensional reference pattern itself can be utilized as part of a watermark message. For example, the ID value of an Arco marker can be used as a verification key for the watermark message, or a sequence of multiple Arco marker ID values ​​can be interpreted as part of the watermark message.

[0093] Implementation method

[0094] FIG. 10 is a block diagram showing the configuration of a watermark insertion device according to an embodiment of the present invention. Referring to FIG. 10, a watermark insertion device (1000) according to an embodiment of the present invention may include an image input unit (1010), a watermark pattern generation unit (1020), a two-dimensional reference pattern generation unit (1030), a pattern position determination unit (1040), a pattern transparency setting unit (1050), a watermark insertion unit (1060), a watermarked image output unit (1070), a processor (1080), and a memory (1090).

[0095] The image input unit (1010) can perform the function of receiving a target image to which a watermark is to be inserted. The target image may be various forms of digital media, such as digital images, video frames, or documents generated by a digital camera, scanner, or computer. The watermark pattern generation unit (1020) performs the function of generating a watermark pattern to be inserted. The watermark pattern may be in the form of data encoded for various purposes, such as copyright information, ownership information, or traceability information. The method of generating the watermark pattern may correspond to any of the frequency domain-based methods, pattern overlay methods, or other various watermark generation methods, and is not limited in the present invention. The two-dimensional reference pattern generation unit (1030) can perform the function of generating a two-dimensional reference pattern to be inserted. As previously described, the two-dimensional reference pattern may be generated based on a suitable variable or ID selected from various forms of patterns such as Arco Marker, AprilTag, WhyCon, and QR code, and an appropriate size, number of bits, and dictionary suitable for the application environment may be determined.

[0096] The pattern positioning unit (1040) can perform the function of determining the position of a two-dimensional reference pattern by considering the characteristics of the target image and / or watermark pattern. The pattern positioning unit (1040) can determine an optimal position that maximizes the pattern recognition rate and minimizes the degradation of visual quality. The pattern positioning unit (1040) may include an algorithm that analyzes the characteristics of the target image to automatically identify an area where the recognition rate of the two-dimensional reference pattern is expected to be high. The pattern transparency setting unit (1050) can perform the function of setting the transparency and visibility of the two-dimensional reference pattern and / or watermark pattern. In this process, an appropriate level of transparency suitable for the application environment can be determined, and the same or independent transparency settings can be made for the watermark pattern and the two-dimensional reference pattern.

[0097] The watermark insertion unit (1060) can perform the function of inserting a watermark pattern and a two-dimensional reference pattern into a target image. The insertion method in this process may be any of the frequency domain-based insertion method, the pattern overlay method, or various other watermark insertion methods. The watermark insertion unit (1060) can insert the watermark pattern and the two-dimensional reference pattern in the same way or in different ways. The watermarked image output unit (1070) can perform the function of outputting an image with a watermark inserted that includes a two-dimensional reference pattern. The outputted image may be stored in digital form, printed, displayed, or transmitted via a network.

[0098] The processor (1080) refers to a central processing unit that controls the operation of each functional unit and performs necessary operations. The processor (1080) may include one or more CPUs, GPUs, or dedicated processors and may be configured to manage the overall operation of the watermark insertion device (1000). The memory (1090) may be configured to perform the function of storing software programs, intermediate processing data, and final results executed by the processor (1080). The memory (1090) may include various forms of storage media such as RAM, ROM, flash memory, and hard disk.

[0099] FIG. 11 is a block diagram showing the configuration of a watermark detection device according to an embodiment of the present invention. Referring to FIG. 11, a watermark detection device (1100) according to an embodiment of the present invention may include an input image acquisition unit (1110), a two-dimensional reference pattern detection unit (1120), a projection transformation estimation unit (1130), a geometric distortion correction unit (1140), a watermark detection unit (1150), a result processing unit (1160), a result output unit (1170), a processor (1180), and a memory (1190).

[0100] The input image acquisition unit (1110) can perform the function of receiving an image with a watermark inserted by capturing or acquiring it. The input image can be acquired through a digital camera, a smartphone, or other image acquisition device, and projection distortion may occur during this process. The two-dimensional reference pattern detection unit (1120) can perform the function of detecting a two-dimensional reference pattern in the input image. In a preferred embodiment of the present invention, an Arco marker detection algorithm can be used to identify Arco markers within the image. In this process, relevant functions of a computer vision library such as OpenCV may be utilized. The projection transformation estimation unit (1130) can perform the function of estimating projection transformation information by analyzing the location and shape of the detected two-dimensional reference pattern. Specifically, a homography matrix is ​​calculated using the corner coordinates of the detected two-dimensional reference pattern, and the homography matrix may be a mathematical expression of the projection transformation relationship from the distorted image plane to the original image plane.

[0101] The geometric distortion correction unit (1140) can perform the function of correcting geometric distortion in the watermark-inserted area using the estimated projection transformation information. In this process, the distorted area is inversely transformed back into its original form using the previously calculated homography matrix. At this time, the inverse transformation can be implemented through an image geometric transformation algorithm such as the warpPerspective function of OpenCV. The watermark detection unit (1150) can perform the function of detecting a watermark in the image where the geometric distortion has been corrected. In this process, a detection algorithm corresponding to the original watermark insertion method can be applied. For example, in the case of a watermark inserted in the frequency domain, the watermark is detected by analyzing the corresponding frequency components after frequency transformation, and in the case of a watermark inserted using a pattern overlay method, the watermark is detected through a pattern matching technique.

[0102] The result processing unit (1160) can perform the function of interpreting and processing the detected watermark message. If necessary, it can verify the watermark message or perform additional information processing by utilizing key values ​​or additional information stored in a two-dimensional reference pattern. The result output unit (1170) can perform the function of outputting the detection result. The output result may include the content of the watermark message, whether detection was successful, and other related information.

[0103] The processor (1180) refers to a central processing unit that controls the operation of each functional unit and performs necessary operations. The processor (1180) may include one or more CPUs, GPUs, or dedicated processors and may be configured to manage the overall operation of the watermark detection device (1100). The memory (1190) may be configured to perform the function of storing software programs, intermediate processing data, and final results executed by the processor (1180). The memory (1190) may include various types of storage media such as RAM, ROM, flash memory, and hard disk.

[0104] According to a preferred embodiment of the present invention, the watermark insertion device (1000) and the watermark detection device (1100) may each be implemented as independent hardware devices. However, the two devices (1000, 1100) may be integrated and implemented on a single hardware platform, in which case some functional parts may be shared.

[0105] According to another embodiment of the present invention, at least one of the watermark insertion device (1000) and / or watermark detection device (1100) may be implemented in software. In this case, each functional part may be implemented as a software module or component that runs on a computer, and the software may be distributed in the form of a computer program product.

[0106] According to another embodiment of the present invention, the watermark detection device (1100) may be implemented in a terminal information processing device including a mobile device, for example, a smartphone or a tablet PC. In this case, an image with a watermark embedded may be captured through the camera of the mobile device, and a watermark detection process may be performed using a built-in processor. Such a mobile implementation may be utilized in various application fields, such as augmented reality applications, product authentication, or digital content access control.

[0107] The processor (1080, 1180) described in this specification may mean one or more general-purpose computers or special-purpose computers, such as a processor, a controller, an arithmetic logic unit (ALU), a digital signal processor, a microcomputer, a field programmable array (FPA), a programmable logic unit (PLU), a microprocessor, or any other device capable of executing and responding to instructions. Even if the processor is expressed in the singular for convenience of understanding, a person skilled in the art will understand that the processor may include a plurality of processing elements and / or a plurality of types of processing elements. For example, a device according to one embodiment of the present invention may include a plurality of processors or one processor and one controller as the processor. Furthermore, the processor may be implemented by various processing configurations, such as a parallel processor or a multi-core processor.

[0108] The processor may be configured to execute an operating system (OS) and one or more software executed on the operating system. Additionally, the processor may access, store, manipulate, process, and generate data in response to the execution of the software.

[0109] The software may include a computer program, code, instructions, or a combination of one or more of these, and may be configured to control the processor to operate as desired and to issue instructions to the processor independently or collectively. The software may be permanently or temporarily embodied in any type of machine, component, physical device, virtual equipment, computer storage medium or device, or transmitted signal wave in order to be interpreted by the processor or to provide instructions or data to the processor. The software may be distributed over networked computer systems and may be stored or executed in a distributed manner.

[0110] The software may also be implemented in the form of program instructions that can be executed through various computer means and may be recorded or stored in the memory (1090, 1190). The memory may be a computer-readable recording medium, and program instructions, data files, data structures, etc. may be recorded on the computer-readable recording medium alone or in combination. The program instructions stored in the memory may be based on a command system specifically designed and configured for embodiments of the present invention, or may follow a command system known and available to those skilled in the art of computer software, such as Assembly, C, C++, Java, Python, etc. It should be understood that the command system and the program instructions thereunder include not only machine code such as that produced by a compiler, but also high-level language code that can be executed by a device and / or processor according to an embodiment of the present invention using an interpreter, etc.

[0111] A computer-readable recording medium constituting an device according to an embodiment of the present invention, including the memory described herein, may include a temporary or volatile recording medium that is maintained only while the processor is operating, such as a processor cache, RAM, or flash memory; or may include a relatively non-volatile or long-term recording medium such as a magnetic media such as a hard disk, floppy disk, and magnetic tape; an optical recording medium such as a CD-ROM or DVD; a magneto-optical media such as a floptical disk; or a solid-state memory; or may include a read-only recording medium such as a ROM placed on hardware; furthermore, the hardware itself, configured to perform operations equivalent to a series of program instructions by a hard-wired structure by circuit wiring, may also be considered as having each step for performing the operation implementing the embodiment of the present invention recorded by the connection and arrangement of the hardware components, so the method of connection and arrangement is equivalent to the memory. It is obvious to an ordinary technician that it can be seen.

[0112] The embodiments described above with respect to the processor and the memory are not mutually exclusive and may be selected or combined as needed. For example, a hardware device may be configured to operate as a module composed of one or more of the software to perform the operation of the embodiments of the present invention, and vice versa. As another example, in this specification, all or part of the operation assigned to a certain functional unit may be implemented by one or more of the software stored in a device according to an embodiment of the present invention (preferably in a recording medium falling within the category of the memory) and configured to be executed by the processor, in which case such a functional unit may be implemented as a functional unit "included" in the processor.

[0113] According to another aspect of the present invention, an article invention comprising image information itself in which a two-dimensional reference pattern and a watermark pattern are inserted may be provided. That is, it is obvious that any form of storing or displaying image information in which a watermark and a two-dimensional reference pattern are inserted, generated in accordance with the method of the present invention, falls within the scope of the rights of the present invention.

[0114] That is, in one embodiment of the present invention, an image information having a watermark pattern and a two-dimensional reference pattern robust against projection distortion is recorded on a recording medium having an information recording area, and the two-dimensional reference pattern is configured to have a structure capable of estimating transformation information regarding projection distortion applied to the image information as described above. The recording medium may include electronic storage media such as a hard disk, flash memory, optical disk, semiconductor memory, magnetic tape, etc., and in some cases may include a form printed or displayed on paper, film, plastic sheet, or other surfaces. Furthermore, display means implemented by LCD, PDP, OLED, and various other means as a medium for temporarily recording and displaying an image also fall within the category of the recording medium envisioned in the present invention. Therefore, in the present invention, the information recording area is not limited in its literal sense and should be interpreted as any means for substantially or informationally displaying, expressing, storing, or recording image information in a specific object; and the recording medium should also be understood as including any object capable of recording or displaying an image.

[0116] As such, a recording medium storing image information with an embedded watermark and a two-dimensional reference pattern inherently embodies the core technical features of the present invention. This enables the stable detection of the watermark by correcting the distortion through the two-dimensional reference pattern, even if projection distortion occurs during the detection process of the stored image information. This provides stronger protection measures for the protection of ownership rights of digital content, prevention of illegal distribution, and copyright management.

[0118] Although the present invention has been described above with reference to the drawings and embodiments, as previously stated, the scope of protection of the present invention is not limited by the drawings or embodiments presented above, and those skilled in the art will understand that various modifications and changes can be made to the present invention without departing from the spirit and scope of the invention as described in the claims of the present invention.

Claims

Claim 1 A method for inserting a watermark signal comprises: receiving a target image to be inserted with a watermark; generating a watermark pattern to be inserted into the target image; generating a two-dimensional reference pattern; determining the position of the two-dimensional reference pattern relative to the watermark pattern; inserting the watermark pattern and the two-dimensional reference pattern into the target image; and outputting an image with the watermark inserted therein; wherein the two-dimensional reference pattern is robust against perspective distortion. Claim 2 A watermark insertion method according to claim 1, characterized in that the two-dimensional reference pattern is one of an ArUco marker, an AprilTag, a WhyCon marker, a ChArUco marker, a QR code, and a DataMatrix. Claim 3 A watermark insertion method according to claim 1, characterized in that the two-dimensional reference pattern is placed in the corner area of ​​the watermark pattern. Claim 4 A watermark insertion method according to claim 1, wherein the two-dimensional reference pattern comprises a plurality of two-dimensional reference patterns, and the plurality of two-dimensional reference patterns have the same key value or different key values. Claim 5 A watermark insertion method according to claim 4, wherein the plurality of two-dimensional reference patterns have different key values, and the different key values ​​are used to indicate the directionality of the watermark pattern. Claim 6 A watermark insertion method according to claim 1, wherein the two-dimensional reference pattern is arranged in a manner that minimizes interference between the target image and the watermark pattern. Claim 7 A watermark insertion method according to claim 6, wherein the step of determining the position of the two-dimensional reference pattern is characterized by determining the position of the two-dimensional reference pattern to minimize interference by avoiding a noise-generating area during printing, and the two-dimensional reference pattern is placed at the said position. Claim 8 A watermark insertion method according to claim 1, further comprising the step of setting the transparency of the two-dimensional reference pattern; wherein the watermark pattern and the two-dimensional reference pattern are arranged to spatially overlap each other. Claim 9 A watermark insertion method according to claim 1, characterized in that the watermark pattern and the two-dimensional reference pattern are arranged so as not to spatially overlap each other. Claim 10 A watermark insertion method according to claim 1, wherein the two-dimensional reference pattern is inserted into the target image in the frequency domain. Claim 11 A watermark insertion method according to claim 1, wherein the two-dimensional reference pattern is inserted in a spatial area of ​​the target image. Claim 12 A watermark insertion method according to claim 1, characterized in that the two-dimensional reference pattern is configured to encode and represent at least a portion of the information represented by the watermark pattern. Claim 13 A watermark insertion method according to claim 1, wherein the step of generating the watermark pattern generates a watermark pattern that is displayed as at least one two-dimensional reference pattern, and the step of generating the two-dimensional reference pattern is configured to generate a two-dimensional reference pattern that constitutes at least a part of the watermark by the watermark pattern. Claim 14 A watermark insertion method according to claim 1, wherein the image to be inserted is unfolded in a three-dimensional space, the watermark pattern is configured to be recognized by being displayed on at least one surface in the three-dimensional space, and the two-dimensional reference pattern is used to specify at least one of the direction, order, and content of the watermark detected from the at least one surface in the three-dimensional space. Claim 15 A watermark detection method comprising: receiving an image to be detected as a watermark; detecting a two-dimensional reference pattern in the image to be detected; calculating perspective distortion information based on at least one of the position and shape of the detected two-dimensional reference pattern; correcting geometric distortion of the image to be detected based on the calculated perspective distortion information; and detecting a watermark from the image to be detected in which geometric distortion has been corrected. Claim 16 A watermark detection method according to claim 15, wherein the step of detecting the two-dimensional reference pattern is characterized by detecting one of the two-dimensional patterns of an ArUco marker, an AprilTag, a WhyCon marker, a ChArUco marker, a QR code, and a DataMatrix. Claim 17 A watermark detection method according to claim 15, wherein the step of calculating projection distortion information is characterized by calculating the projection distortion information by synthesizing information obtained from the plurality of two-dimensional reference patterns when a plurality of two-dimensional reference patterns are detected. Claim 18 A watermark insertion device comprising: a processor; a memory connected to the processor; an image input unit receiving an image to be inserted with a watermark; a watermark pattern generation unit generating a watermark pattern to be inserted into the image Claim 19 A watermark detection device comprising: a processor; a memory connected to the processor; an image input unit receiving an image to be detected as a watermark; a pattern detection unit detecting a two-dimensional reference pattern in the image to be detected; a distortion calculation unit calculating perspective distortion information based on at least one of the position and shape of the detected two-dimensional reference pattern; a distortion correction unit correcting geometric distortion of the image to be detected based on the calculated perspective distortion information; and a watermark detection unit detecting a watermark from the image to be detected in which geometric distortion has been corrected. Claim 20 A recording medium having an information recording area, wherein the information recording area has image information in which a two-dimensional reference pattern robust against a watermark pattern and perspective distortion is inserted, and the two-dimensional reference pattern has a structure capable of estimating transformation information regarding the perspective distortion applied to the image information.

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