Device and method for signing metadata frame corresponding to image frame of sequence of image frames

Abstract

To provide a device and a method of signing a metadata frame corresponding to an image frame of a sequence of image frames, and a non-transitory computer-readable storage medium.SOLUTION: In a method 100 for signing metadata, a device acquires a sequence of an image frame (S102), detects an object in the image frame of the sequence of the image frame (S104), forms a metadata frame on the basis of the detected object in the image frame (S106), generates a digital signature on the basis of at least a subset of the metadata in the metadata frame (S110), and adds additional metadata to the metadata frame (S120). The metadata frame comprises metadata of one or more detected objects in the image frame, and the metadata comprises coordinates defining a location in the image frame of the object.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to the authentication of metadata, and more particularly to signing metadata frames corresponding to image frames of a sequence of image frames.

Background Art

[0002] In some applications, it is desirable to verify that the metadata of each metadata frame, which corresponds to each image frame of a sequence of image frames, is intact, i.e., has not been tampered with after generation, and that the metadata is from a genuine source. One way to enable such verification for metadata corresponding to a sequence of image frames is to generate a digital signature for the metadata frame. The digital signature is then transmitted within the header of the metadata stream containing the metadata frame and can be used on the receiver side to verify that the metadata of the metadata frame is intact and that the digital signature was generated by a genuine source. However, if digital signatures are generated for all metadata frames in relation to a sequence of image frames, all metadata frames will be considered not intact or received from a non-genuine source if they cannot verify the digital signature. Thus, a change in a single metadata frame affects multiple metadata frames within a stream segment being considered non-genuine and untrustworthy. There is a need for an improved method for signing metadata with respect to this problem.

Summary of the Invention

[0003] An object of the present invention is to facilitate the enhancement of signing and transmission of metadata corresponding to a sequence of image frames.

[0004] According to a first aspect, a method is provided for signing metadata frames corresponding to image frames in a sequence of image frames. The metadata frame contains metadata for one or more detected objects within the image frame. Furthermore, the metadata for each detected object includes coordinates defining the location of the detected object within the image frame. The method includes generating a digital signature based on at least a subset of the metadata in the metadata frame, and adding additional metadata to the metadata frame, wherein the additional metadata includes the digital signature and predefined coordinates defining that the additional metadata contains the digital signature.

[0005] Metadata frames can be authenticated separately by generating a separate digital signature for each metadata frame. Furthermore, by including the digital signature as additional metadata within the metadata frame and using predefined coordinates to indicate that the additional metadata contains the digital signature, digital signatures can be transmitted to each metadata frame without the need to conform to the metadata frame format, i.e., the format in which the metadata is represented, and without the need to conform to the protocol for transmitting the metadata. Instead, the receiving device can recognize the predefined coordinates that indicate that the additional metadata contains the digital signature. The receiving device only needs to recognize the predefined coordinates once, and this can be done offline. Moreover, the digital signature can be transmitted within the metadata frame, and the digital signature will be used for authentication against this metadata frame. This is more efficient and discrete than transmitting the digital signature separately from the metadata frame.

[0006] A digital signature refers to any type of digital signature that allows for the verification of an authenticity metadata frame.

[0007] Predefined coordinates can be reserved specifically for specifying that additional metadata includes a digital signature. This also means that it is impossible to use the predefined coordinates as coordinates for an actual object. By selecting such dedicated coordinates, there is no risk that a detected object will have predefined coordinates, and therefore the metadata of that detected object will be interpreted as a digital signature.

[0008] Predefined coordinates can define the position of an object that does not have extension. This eliminates the risk that the detected object will have predefined coordinates, since the detected object will have extension.

[0009] The coordinates can represent, for example, the top-left and bottom-right corners of the bounding box associated with the detected object, and the predefined coordinates represent the same coordinates for the top-left and bottom-right corners. This eliminates the risk that the detected object will have different coordinates for its top-left and bottom-right corners, thus preventing the detected object from having predefined coordinates.

[0010] In the process of generating a digital signature, the digital signature may be generated based on the private key of a public-private key pair.

[0011] The operation of generating a digital signature may include hashing at least a subset of the metadata, thereby generating a hash, and then generating a digital signature based on that hash.

[0012] The metadata for each detected object may be represented as a separate item within a metadata frame, each separate item containing coordinates that define the position of the detected object within the image frame, and any additional metadata may be represented as additional separate items.

[0013] Additional metadata can use the same syntax as the metadata for each detected object.

[0014] The method may further include forming a metadata frame based on the objects detected within the image frame.

[0015] The method may further include obtaining a sequence of image frames and detecting objects within the image frames of the sequence of image frames.

[0016] According to a second aspect, a method is provided for authenticating a digitally signed metadata frame corresponding to an image frame in a sequence of image frames. The metadata frame contains metadata for one or more detected objects within the image frame. The metadata for each detected object contains coordinates that define the location of the detected object within the image frame. Furthermore, the metadata frame further includes additional metadata containing digital signatures for at least a subset of the metadata within the metadata frame, and predefined coordinates that define the additional metadata as containing digital signatures. The method includes identifying the predefined coordinates that define the additional metadata as containing digital signatures, extracting the digital signatures from the additional metadata, and authenticating the metadata frame based on the digital signatures.

[0017] By including a digital signature as additional metadata within the metadata frame, and by using predefined coordinates to indicate that the additional metadata contains a digital signature, the digital signature can be identified for authentication of the metadata frame without the need to conform to a protocol for transmitting the metadata, and without the need to conform to the format of the metadata frame, i.e., the format in which the metadata is represented, and the digital signature can be extracted at the receiver. Instead, the receiving device only needs to be aware of the predefined coordinates that indicate that the additional metadata contains a digital signature. The receiving device only needs to be aware of the predefined coordinates once, and this can be done offline.

[0018] According to a third aspect, a non-temporary computer-readable storage medium is provided that stores instructions for implementing the method according to the first or second aspect when executed on a device having at least one processor.

[0019] According to a fourth aspect, a device is provided for signing metadata frames corresponding to image frames in a sequence of image frames. The metadata frame contains metadata for one or more detected objects within the image frame. Furthermore, the metadata for each detected object includes coordinates defining the location of the detected object within the image frame. The device includes a generating function configured to generate a digital signature based on at least a subset of the metadata in the metadata frame, and an additional function configured to add additional metadata to the metadata frame, wherein the additional metadata includes a digital signature and predefined coordinates defining that the additional metadata contains a digital signature.

[0020] The generation function may be configured to hash at least a subset of the metadata, thereby generating a hash, and then generate a digital signature based on the hash.

[0021] The circuit may be further configured to perform a shaping function configured to form a metadata frame based on detected objects within the image frame.

[0022] The circuit may be further configured to perform an acquisition function configured to acquire a sequence of image frames, and a detection function configured to detect objects within the image frames of the sequence of image frames.

[0023] The optional additional features of the method relating to the first embodiment, as mentioned above, also apply to the device relating to the fourth embodiment, when applicable. References above are made to avoid unnecessary repetition.

[0024] Further scope of applicability of the present invention will become apparent from the detailed description given below. However, the detailed description and specific examples are given only as illustrations, as they illustrate preferred embodiments of the invention and various changes and modifications within the scope of the invention will become apparent to those skilled in the art from this detailed description.

[0025] Therefore, it should be understood that the present invention is not limited to specific component parts of such devices or the operations of such methods, as the described devices and methods can be variable. It should also be understood that the terms used herein are for the purpose of describing particular embodiments only and are not intended to be limiting. It should be noted that, as used in the specification and the appended claims, the articles "a", "an", "the", and "said" are intended to mean that one or more of the elements are present, unless the context clearly dictates otherwise. Thus, for example, references to "a unit" or "the unit" can include several devices, and the like. Further, the words "comprising", "including", "containing", and similar words do not exclude other elements or steps.

[0026] The above and other aspects of the present invention will now be described in more detail with reference to the accompanying drawings. The drawings should not be considered limiting, but rather are used for explanation and understanding.

Brief Description of the Drawings

[0027] [Figure 1] It is a flowchart related to an embodiment of a method for signing metadata corresponding to an image frame of a sequence of image frames. [Figure 2] It is a flowchart related to an embodiment of a method for authenticating a digitally signed metadata frame corresponding to an image frame of a sequence of image frames. [Figure 3] It is a schematic diagram related to an embodiment of a device for signing metadata corresponding to an image frame of a sequence of image frames. [Figure 4] It is a schematic diagram related to an embodiment of a device for authenticating a digitally signed metadata frame corresponding to an image frame of a sequence of image frames.

Best Mode for Carrying Out the Invention

[0028] The present invention will now be described below with reference to the accompanying drawings, in which the presently preferred embodiments of the invention are illustrated. However, the invention can be embodied in many different forms and should not be construed as limited to the embodiments set forth herein.

[0029] Embodiments of the invention may be used to verify the authenticity of metadata to ensure that the metadata has not been compromised, i.e., altered after generation and comes from a genuine source, in applications where a metadata frame corresponds to an image frame of a sequence of image frames, each metadata frame contains metadata related to one or more objects detected within the corresponding image frame, and the position of each object is defined by means of object coordinates. Metadata is typically generated using analysis of the image frames and may be further related to additional analysis information such as, for example, object id, object class, object color. Metadata may also relate to other things than objects, such as information related to audio, radar, etc. The format and syntax used to represent metadata are predefined, for example, by standard means, so that both the transmitter and the receiver recognize the format and syntax. One standard for metadata representation and transmission is ONVIF Profile M. An example of what metadata according to ONVIF Profile M might look like for one metadata frame containing metadata for one object is shown below. TIFF2023177292000002.tif133170

[0030] The tag "BoundingBox" is used to represent the image coordinates of the bounding box for the detected object. In this embodiment, the coordinates for the object with ID 12 are represented by a bounding box with image coordinates (20,180) for the top-left corner and (30,100) for the bottom-right corner. If the frame contained further objects, metadata for such further objects was included in relation to objects with different IDs, i.e., different values ​​for the tag "ObjectId".

[0031] On the receiver side, including the decoder, a digital signature on the metadata frame can be used to verify the authenticity of the metadata frame. For example, if a digital signature on the metadata frame is created by encrypting the hash of at least a portion of the metadata frame using the private key of a public-private-key pair, then the metadata can be verified to be undamaged and from an authentic source by decrypting the digital signature using the public key of the public-private-key pair and comparing the result to the corresponding hash of at least a portion of the metadata frame as received on the receiver side. If they are equal, the metadata frame is undamaged and from an authentic source; if they are not equal, the metadata frame is either damaged (altered / tampered with) or does not come from an authentic source.

[0032] Hereinafter, an embodiment of method 100 for signing metadata frames corresponding to image frames in a sequence of image frames is discussed with reference to Figure 1. The metadata frame contains metadata for one or more detected objects within the image frame. Furthermore, the metadata for each detected object includes coordinates that define the location of the detected object within the image frame. Method 100 includes generating a digital signature (S110) based on at least a subset of the metadata in the metadata frame, and adding additional metadata to the metadata frame (S120). The additional metadata includes the digital signature and predefined coordinates that define that the additional metadata contains the digital signature. This differs from the prior art where the digital signature is transmitted, for example, in the header of a metadata stream and is relevant to all metadata frames in the metadata stream. By including the digital signature as additional metadata within the metadata frame and using predefined coordinates to indicate that the additional metadata contains the digital signature, each metadata frame can carry its own digital signature. Furthermore, the predefined coordinates allow the digital signature to be identified for authentication of the metadata frame without the need to conform to a protocol for transmitting the metadata, and the digital signature can be retrieved at the receiver. This can be achieved without the need to conform to the metadata frame format, i.e., the format in which the metadata is represented. Instead, the receiving device only needs to recognize predefined coordinates that specify that the additional metadata includes a digital signature. The receiving device only needs to recognize these predefined coordinates once, and this can be done offline.

[0033] The fact that a digital signature is based on "at least a subset" of the metadata within a metadata frame means that the digital signature only needs to be based on the metadata of the metadata frame that makes it verifiable. For example, a digital signature may be based on metadata relevant to only a subset of objects found within the frame. For instance, it may be determined that only the metadata for one or more specific types of objects needs to be verifiable. In such cases, a digital signature may be generated based on the metadata relevant to those one or more specific types of objects.

[0034] It will be understood that the predefined coordinates are also known to the device receiving the metadata frame. The receiving device interprets the metadata according to the predefined format and syntax used. When interpreting additional metadata, the receiving device identifies the coordinates as those that specify that the additional metadata contains a digital signature.

[0035] The predefined coordinates are preferably static, i.e., the same predefined coordinates are used over time to specify that additional metadata includes a digital signature. Alternatively, the predefined coordinates may be variable over time, in such a way that the receiving device knows which coordinates are used in relation to each metadata frame.

[0036] The predefined coordinates may be reserved exclusively for specifying that additional metadata includes a digital signature, that is, the predefined coordinates may not be used as coordinates for the actual object. By selecting such reserved coordinates, there is no risk that the actual object will have the predefined coordinates and therefore the metadata of the actual object will be interpreted as a digital signature. Method 100 may further include the action of selecting predefined coordinates and the action of reserving the predefined coordinates exclusively for specifying that additional metadata includes a digital signature.

[0037] Furthermore, if the predefined format and syntax used to represent the metadata require additional metadata to specify an object in order to include coordinates, a dummy object may be identified using a different identifier than all the actual objects identified within the metadata frame for which the metadata is provided. Thus, the additional metadata may further include an object ID, and predefined coordinates associated with that object ID may be indicated.

[0038] To implement a specific, predefined coordinate system, the predefined coordinates may not be related to actual objects. For example, predefined coordinates may define the position of an object without extension. For instance, if the coordinates represent the top-left and bottom-right corners of a bounding box associated with a detected object, such as in the ONVIF profile M, the predefined coordinates will have the same coordinates for the top-left corner as for the bottom-right corner. This is also applicable when using different formats and syntaxes where the bounding box is defined by the top-right and bottom-left corners. In another example, the coordinates may represent the top-left corner and the distance to the bottom-right corner. To define the position of an object without extension, the predefined coordinates will have an indication of an arbitrary coordinate for the top-left corner and a distance of zero to the bottom-right corner. This is also applicable when the bounding box is defined by the coordinates of any of the other corners and the distance from that corner to the corners diagonally across the bounding box. Predefined coordinates may be identical over time, or they may be variable insofar as they indicate an object without extension, i.e., a bounding box with zero pixels.

[0039] Other alternatives for achieving specific, predefined coordinates are also conceivable. For example, the predefined coordinates might be such that the object has negative extension, for instance, the top-left corner is positioned below and / or to the right of the bottom-right corner. In another example, the predefined coordinates might be such that the object is positioned entirely or partially outside the image frame, for example, the top-left corner and / or bottom-right corner are positioned outside the image frame.

[0040] The advantage of using predefined coordinates that cannot be associated with actual objects is that if a device receiving the metadata frame does not recognize the predefined coordinates, it cannot interpret them as being associated with an object, and therefore simply ignores the additional metadata.

[0041] A digital signature can be any type of digital signature that allows for verification of its authenticity. For example, a digital signature can be generated based on the private key of a public-private key pair. For example, RSA (Rivest-Shamir-Adleman) 256-bit encryption, the Digital Signature Algorithm (DSA), and the Elliptic Curve Digital Signing Algorithm (ECDSA) can be used to generate digital signatures. A digital signature on a metadata frame can be generated by applying the private key to the metadata of the metadata frame or a subset of the metadata. However, to reduce the size of the digital signature, the metadata may first be hashed by means of a hash function, such as a cryptographic hash function, to generate a hash (S112). The digital signature can then be generated based on the hash, for example, by applying the private key to the hash (S114). Examples of cryptographic hash functions include MD5, SHA-1, SHA-2 (SHA-256 / SHA-512), SHA-3, and BLAKE-3.

[0042] The metadata for each detected object may be represented as a separate item within a metadata frame, and each separate item contains coordinates that define the position of the detected object within the image frame. For example, for metadata according to the ONVIF profile M illustrated above, the item associated with the object is the metadata "<tt:Object ObjectId”12”> It is located between the line that states " and the line that states "<tt:Object ObjectId”12”> This includes lines stating " and lines stating ". In such cases, additional metadata may also be represented as an additional separate item using the same format and syntax.

[0043] The additional metadata may use the same syntax and / or format as the metadata of each detected object. Therefore, the syntax and / or format used for the detected object is also used for the additional metadata. Thus, the additional metadata is interpreted as metadata associated with the object, and the receiving device can interpret the additional data. When the receiving device identifies predefined coordinates, the receiving device can interpret the additional metadata as including a digital signature.

[0044] For example, if additional metadata is added as metadata associated with an object according to ONVIF profile M, the tag "BoundingBox" could contain left="20.0" top="180.0" right="20.0" bottom="180.0", or any other coordinates indicating a bounding box of zero pixels without expansion. The digital signature could then be included in the same position as the tag "Type", i.e., "Vehicle", in the example metadata frame according to ONVIF profile M as described above.

[0045] Digital signatures can be included in additional metadata using existing variables or tags, following the syntax and format used for metadata frames, which are used to provide metadata about several other characteristics of an object. The only requirement is that the existing variables or tags are permitted to contain a sufficient number of bits to enclose the digital signature. The receiving device then needs to recognize that the existing tags or variables are used to enclose the digital signature in the additional metadata when the predefined coordinates are identified. Alternatively, a new variable or tag, such as "Digital Signature" or similar, may be added.

[0046] Method 100 may further include obtaining a sequence of image frames (S102). The sequence of image frames may be obtained by capturing the sequence of image frames by the camera if Method 100 is performed on a camera (S102). Alternatively, the sequence of image frames may be obtained by receiving it directly from the camera, or via another device if Method is performed on a device separate from the camera (S102).

[0047] Method 100 may further include detecting objects within image frames of a sequence of image frames (S104). The objects may be detected using any type of object detection method.

[0048] Method 100 may further include forming a metadata frame based on detected objects within an image frame (S106). Forming the metadata frame may be based on information from the object detection method and / or further analysis of the detected objects.

[0049] Even when a digital signature is described in relation to a single metadata frame, the digital signature may be contained within a metadata frame that relates to two or more metadata frames, for example, a sequential metadata frame relating to all image frames of a group of pictures (GOP). The digital signature is then based on at least a subset of the metadata in each metadata frame.

[0050] Hereinafter, an embodiment of method 200 for authenticating a digitally signed metadata frame corresponding to an image frame in a sequence of image frames is discussed with reference to Figure 2. The metadata frame contains metadata for one or more detected objects within the image frame. The metadata for each detected object contains coordinates that define the location of the detected object within the image frame. Furthermore, the metadata frame contains additional metadata that includes a digital signature for at least a subset of the metadata within the metadata frame, and predefined coordinates that define the additional metadata as containing the digital signature. In other words, the metadata frame is a metadata frame such as the one produced by method 100 as described with reference to Figure 1. Method 200 includes identifying predefined coordinates that define the additional metadata as containing the digital signature (S210). The digital signature is then extracted from the additional metadata (S220), and at least a subset of the metadata is authenticated based on the digital signature (S230). How the digital signature is used to authenticate the metadata frame (verify the authenticity of the metadata frame) depends on the type of digital signature used. For example, a digital signature on a metadata frame could be created by applying the private key of a public-private-key pair to hash at least a portion of the metadata frame. The authenticity of the metadata frame can then be verified by decrypting the digital signature using the public key of the public-private-key pair and comparing the result with the corresponding hash of at least a portion of the metadata frame as received within the metadata frame. The same hash function used to generate the hash on which the digital signature is based should be used to generate hashes from at least a subset of the metadata as received. If they are equal, the authenticity of the metadata frame is verified, i.e., the metadata frame is not corrupted and comes from an authentic source. If they are not equal, the authenticity of the metadata frame is not verified, and the metadata frame is either corrupted or does not come from an authentic source.

[0051] Hereinafter, an embodiment of device 300 for signing metadata corresponding to image frames in a sequence of image frames is discussed with reference to Figure 3. The metadata frame contains metadata for one or more detected objects within the image frame. Furthermore, the metadata for each detected object includes coordinates that define the location of the detected object within the image frame. Device 300 includes circuit 310. Circuit 310 is configured to perform the functions of device 300. Circuit 310 may include a processor 312, such as a central processing unit (CPU), microcontroller, or microprocessor. The processor 312 is configured to execute program code. The program code may be configured, for example, to perform the functions of device 300.

[0052] Device 300 may further include memory 330. Memory 330 may be one or more of a buffer, flash memory, hard drive, removable media, volatile memory, non-volatile memory, random access memory (RAM), or another suitable device. In a typical configuration, memory 330 may include non-volatile memory for long-term data storage and volatile memory that serves as system memory for circuit 310. Memory 330 may exchange data with circuit 310 over a data bus. Accompanying control lines and address buses may also exist between memory 330 and circuit 310.

[0053] The functionality of device 300 may be embodied in the form of executable logic routines (e.g., lines of code, software programs, etc.), which are stored in a non-temporary computer-readable medium of system 300 (e.g., memory 330) and executed by circuit 310 (e.g., using processor 312). Furthermore, the functionality of a system device may be a standalone software application or may form part of a software application that performs additional tasks related to the system device. The functionality described may be considered as a method configured to be performed by a processing unit, e.g., the processor 312 of circuit 310. The functionality described may also be implemented in software, and such functionality may also be implemented through dedicated hardware or firmware, or any combination of hardware, firmware, and / or software.

[0054] Circuit 310 is configured to perform a generation function 331 which is configured to generate a digital signature using at least a subset of the metadata in the metadata frame.

[0055] Circuit 310 is further configured to perform an additional function 332 configured to add additional metadata to the metadata frame, the additional metadata including a digital signature and predefined coordinates that specify that the additional metadata includes the digital signature.

[0056] The generation function 331 may be configured to hash at least a subset of the metadata, thereby generating a hash, and to generate a digital signature based on the hash.

[0057] The circuit 310 may be further configured to perform an acquisition function 333 configured to acquire a sequence of image frames, and a detection function 334 configured to detect objects within the image frames of the sequence of image frames.

[0058] The circuit 310 may be further configured to perform a forming function 335 configured to form a metadata frame based on detected objects within the image frame.

[0059] Device 300 may be implemented in a single physical unit, and as a result, all of its functions may be implemented in that single physical unit. Alternatively, device 300 may be implemented in more than one physical unit, and as a result, its functions may be implemented in two or more different physical units.

[0060] The function performed by circuit 310 can be further adapted as a corresponding step in an embodiment of the method described in relation to Figure 1.

[0061] Hereinafter, an embodiment of device 400 for authenticating digitally signed metadata frames corresponding to image frames in a sequence of image frames is discussed with reference to Figure 4. Figure 4 shows a schematic diagram relating to an embodiment of device 400. The metadata frame contains metadata for one or more detected objects within the image frame. The metadata for each detected object includes coordinates that define the location of the detected object within the image frame. Furthermore, the metadata frame further includes additional metadata that contains digital signatures for at least a subset of the metadata, and predefined coordinates that define that the additional metadata contains digital signatures. Device 400 includes circuitry 410. Circuitry 410 is configured to perform the functions of device 400. Circuitry 410 may include a processor 412, such as a central processing unit (CPU), a microcontroller, or a microprocessor. The processor 412 is configured to execute program code. The program code may be configured, for example, to perform the functions of device 400.

[0062] Device 400 may further include memory 430. Memory 430 may be one or more of a buffer, flash memory, hard drive, removable media, volatile memory, non-volatile memory, random access memory (RAM), or another suitable device. In a typical array, memory 430 may include non-volatile memory for long-term data storage and volatile memory that serves as system memory for circuit 410. Memory 430 may exchange data with circuit 410 over a data bus. Accompanying control lines and address buses may also exist between memory 430 and circuit 410.

[0063] The functionality of device 400 may be embodied in the form of executable logic routines (e.g., lines of code, software programs, etc.), which are stored in a non-temporary computer-readable medium of system 400 (e.g., memory 430) and executed by circuit 410 (e.g., using processor 412). Furthermore, the functionality of a system device may be a standalone software application or may form part of a software application that performs additional tasks related to the system device. The functionality described may be considered as a method configured to be performed by a processing unit, e.g., the processor 412 of circuit 410. The functionality described may also be implemented in software, and such functionality may also be implemented through dedicated hardware or firmware, or any combination of hardware, firmware, and / or software.

[0064] Circuit 410 is configured to perform an identification function 431 configured to identify predefined coordinates that specify that additional metadata includes a digital signature.

[0065] Circuit 410 is further configured to perform an extraction function 432 configured to extract a digital signature from additional metadata.

[0066] Circuit 410 is further configured to perform an authentication function 433, which is configured to authenticate a metadata frame based on a digital signature.

[0067] By including a digital signature as additional metadata within the metadata frame, and by using predefined coordinates to indicate that the additional metadata includes a digital signature, the digital signature at the predefined coordinates can be identified for authentication of the metadata frame without the need to conform to a protocol for transmitting the metadata, and without the need to conform to the format of the metadata frame, i.e., the format in which the metadata is represented, and the digital signature can be retrieved at the receiver. Instead, device 400 only needs to recognize the predefined coordinates that indicate that the additional metadata includes a digital signature. Device 400 only needs to recognize the predefined coordinates once, and this can be done offline.

[0068] The authentication function 433 may be configured to hash at least a subset of the received metadata, thereby generating a hash, decrypting the digital signature, and comparing the hash to the decrypted digital signature. If they are equal, the metadata frame is authenticated, i.e., the metadata frame is undamaged and comes from an authentic source. If they are not equal, the metadata frame is either damaged or does not come from an authentic source.

[0069] Device 400 may be implemented in a single physical unit, and as a result, all of its functions may be implemented in that single physical unit. Alternatively, device 400 may be implemented in more than one physical unit, and as a result, its functions may be implemented in two or more different physical units.

[0070] The function performed by circuit 410 can be further adapted as a corresponding step in an embodiment of the method described in relation to Figure 2.

Claims

1. 1. A method of signing a metadata frame corresponding to an image frame of a sequence of image frames, the metadata frame including metadata of one or more detected objects within the image frame, the metadata of each detected object including coordinates defining a position of the detected object within the image frame, the method comprising: generating a digital signature based on at least a subset of the metadata in the metadata frame; adding additional metadata to the metadata frame, the additional metadata including the digital signature and predefined coordinates that specify that the additional metadata includes the digital signature; A method comprising:

2. The method of claim 1 , wherein the predefined coordinates are dedicated to defining that the additional metadata includes the digital signature.

3. The method of claim 1 , wherein the predefined coordinates define a position of an object that has no extension.

4. The method of claim 1 , wherein the coordinates represent an upper left corner and a lower right corner of a bounding box associated with the detected object, and the predefined coordinates represent the same coordinates for the upper left corner and the lower right corner.

5. The method of claim 1 , wherein in the act of generating a digital signature, the digital signature is generated based on a private key of a public and private key pair.

6. The act of generating a digital signature comprises: hashing the at least a subset of the metadata, thereby generating a hash; generating the digital signature based on the hash; The method of claim 1 , comprising:

7. 2. The method of claim 1 , wherein the metadata for each detected object is represented as a separate item in the metadata frame, each separate item including the coordinates defining the position of the detected object in the image frame, and the additional metadata is represented as an additional separate item.

8. The method of claim 1 , wherein the additional metadata uses the same syntax as the metadata for each detected object.

9. forming the metadata frame based on the one or more detected objects in the image frame; The method of claim 1 further comprising:

10. acquiring said sequence of image frames; detecting one or more objects within the image frames of the sequence of image frames; The method of claim 9 further comprising:

11. 1. A method of authenticating a digitally signed metadata frame corresponding to an image frame of a sequence of image frames, said metadata frame including metadata of one or more detected objects within said image frames, said metadata for each detected object including coordinates defining a position of said detected object within said image frame, said metadata frame further including additional metadata including a digital signature for at least a subset of said metadata in said metadata frame and predefined coordinates defining that said additional metadata includes said digital signature, said method comprising: identifying the predefined coordinates, the additional metadata defining the digital signature; deriving the digital signature from the additional metadata; and authenticating the metadata frame based on the digital signature; A method comprising:

12. A non-transitory computer-readable storage medium having stored thereon instructions for implementing the method of any one of claims 1 to 10 and 11 when executed on a device having at least one processor.

13. 1. A device for signing a metadata frame corresponding to an image frame of a sequence of image frames, the metadata frame including metadata of one or more detected objects within the image frames, the metadata of each detected object including coordinates defining a position of the detected object within the image frame, the device comprising: a generating function configured to generate a digital signature using at least a subset of the metadata in the metadata frame; an add function configured to add additional metadata to the metadata frame, the additional metadata including the digital signature and predefined coordinates that specify that the additional metadata includes the digital signature; A device comprising circuitry configured to perform the steps of:

14. The generating function is hashing the at least a subset of the metadata, thereby generating a hash; Generate the digital signature based on the hash. The device of claim 13 configured as follows:

15. The circuit comprises: a forming function configured to form the metadata frame based on the detected object in the image frame; 15. The device of claim 13 or 14, further configured to:

16. The circuit comprises: an acquisition function configured to acquire the sequence of image frames; a detection function configured to detect an object within an image frame of the sequence of image frames; 15. The device of claim 13 or 14, further configured to:

Images