Method and system for producing and checking a security document

Abstract

A method for producing a document having a document body and a visually imperceptible security feature joined to the document body comprises providing a key pair (104) comprising a public and a private key, encrypting (106) data that are unique to the document using the public key of the key pair, and coding (108) the encrypted data into a graphical code. The method furthermore comprises providing (110) a photograph to be joined to the document, embedding (112) the graphical code into the photograph, and joining (114) the photograph and the graphical code embedded therein to the document body.

Description

Area

[0001] The invention relates to a method for producing a document, in particular a valuable or security document, for example, an identification document, as well as a method and a system for verifying the document produced using the method according to the invention. The invention is based on a document formed by a product carrier or document body on and / or in which a multicolored area, for example, a color photograph, is located. background

[0002] A variety of documents are equipped with security features designed to make counterfeiting more difficult or even impossible. These documents include, in particular, valuable or security documents, which serve to verify a person's identity, for example, when crossing a national border, the origin or originality of an item, or a claim, for example, for payment of a sum of money or for the release of a product or provision of a service.

[0003] Forgery can be made more difficult or even prevented, for example, by manufacturing such documents, such as banknotes, from a material that is not readily available. Additionally or alternatively, security features can be created using special inks, such as luminescent or optically variable inks, optical elements such as holograms, tilting images, cinematic objects, lens or prism arrays, guilloche patterns with visible inks or luminescent inks, mottled fibers, security threads, and the like.

[0004] The security features used in valuable or security products can serve exclusively to prove the authenticity of the documents, regardless of their type or user. Individualizing, for example, personalizing, security features also contain, in coded form or in plain text, information about the type of document, the owner or user of this document (i.e., personalization data), and / or about an item, object, or entity to which the document is uniquely assigned. Such information can be a portrait or photo of the user, their personal data, such as their name, date of birth, place of birth, address, or a personal identifier, such as a membership number, or even their signature.Another security feature that individualises the valuable or security product can be, for example, a serial number of the product or the chassis number of a motor vehicle to which the product is assigned.

[0005] US 2018 / 0186167 A1 describes a system capable of generating identifications containing characteristic line patterns corresponding to different portions of secure customer information. Data indicative of one or more linear patterns and data indicative of customer information to be embedded in an identification document are obtained. Respective subsets of the customer information are associated with each of the one or more linear patterns. A photographic image to be incorporated into the identification document is then modified based at least on generating a portion of the photographic image composed of at least one of the one or more linear patterns. The modified photographic image is then placed on an identification document to provide embedded customer information.

[0006] WO 2017 / 148704 A1 describes a security document with a first security element, which comprises a visually recognizable and in particular machine-readable first piece of information, and a second security element, which comprises in particular machine-readable second piece of information, which can be used to verify the first piece of information. Summary

[0007] There is a constant need to integrate, in particular, individualising, for example personalising, security features into products, e.g. documents, which are protected against forgery and / or falsification and / or copying.

[0008] To this end, the security feature should preferably be located in an internal product layer that is secure against counterfeiting, falsification, and / or copying. The security feature integrated into the product should also be inexpensive, easy, and quick to verify. Above all, complex material development should be eliminated, meaning the security feature should be able to be integrated into the product using known substances and devices, such as printers. Ideally, it should be ensured that a colored, especially multi-colored, security feature can be integrated into the product without recalibrating individual colors using an existing color management system for CMYK colors.

[0009] The invention is therefore based on the object of proposing a document with such a security feature which makes manipulation more difficult.

[0010] Furthermore, the invention is based on the object of proposing a method for producing such a document which offers increased security against manipulation.

[0011] Furthermore, the invention is based on the object of proposing a method for checking a document according to the invention, as well as a system set up for the check. Definitions:

[0012] Where the terms "document," "product," "value or security product," and in particular the term "value or security document" are used in the description and claims of this application, these are to be understood as synonymous and include, for example, an identification document, such as a passport, identity card, driver's license or other ID card or access control card, a vehicle registration document, vehicle registration certificate, visa, check, means of payment, in particular a banknote, a check, bank, credit, or cash payment card, customer card, health card, chip card, company ID, proof of authorization, membership card, gift or shopping voucher, waybill or other proof of authorization, tax stamps, postage stamps, tickets, (gaming) tokens, adhesive labels (e.g., for product security), or another ID document. The product can be, for example, a smart card.The security or valuable document can be in ID 1, ID 2, ID 3, or any other format, for example, in booklet form, similar to a passport-like item. A valuable or security product can be a laminate consisting of multiple document layers that are bonded together, e.g., fused, in a precise and / or accurate register, using heat and increased pressure. These products should meet standardized requirements, such as ISO 10373, ISO / IEC 7810, and ISO 14443. The product layers consist, for example, of a carrier material suitable for lamination. In addition to valuable or security documents, the term "value or security product" also includes patches, labels, and the like, which, as security elements, are components of documents and are or become permanently bonded to the document carrier or document body, forming the security feature there.

[0013] The valuable or security product can be formed from a polymer selected from a group comprising polycarbonate (PC), in particular bisphenol A polycarbonate, polyethylene terephthalate (PET), and their derivatives, such as glycol-modified PET (PETG), polyethylene naphthalate (PEN), polyvinyl chloride (PVC), polyvinyl butyral (PVB), polymethyl methacrylate (PMMA), polyimide (PI), polyvinyl alcohol (PVA), polystyrene (PS), polyvinylphenol (PVP), polypropylene (PP), polyethylene (PE), thermoplastic elastomers (TPE), in particular thermoplastic polyurethane (TPU), acrylonitrile-butadiene-styrene copolymer (ABS), and their derivatives, and / or paper and / or cardboard and / or glass and / or metal and / or ceramic. Furthermore, the product can also be made from several of these materials. It is preferably made of PC, PET, and / or PVC. The polymers can be either filled or unfilled. In the latter case, they are preferably transparent or translucent.If the polymers are filled, they are opaque. The above information applies both to films to be bonded together and to liquid formulations that are applied to a precursor, such as a protective or topcoat. The document is preferably produced from a plurality of material layers or films, approximately from 3 to 12, preferably from 4 to 10 films, preferably using a lamination process in which the films are fused together under the influence of pressure and heat. The individual films can consist of the same material or of different materials. Furthermore, production of the document can include forming overlay layers. Overlay layers formed in this way protect a security feature arranged underneath and / or impart the required abrasion resistance to the document.

[0014] Data that is unique to the document refers, in particular, to personalization data that uniquely identifies the owner of the document, i.e., is unique to the owner and thus to the document. Furthermore, the data that is unique to the document can include, for example, information about the type of document and / or about an item, object, or entity to which the document is uniquely assigned. Furthermore, the data that is unique to the document can include, for example, a document ID, such as a serial number.

[0015] Where the terms "individualized" and "individualizing" are used below, they refer to a property of a valuable or security document that allows the document to be assigned to a specific subject (person, animal, object). Where the terms "personalized" and "personalizing" are used below, they refer to the property of a valuable or security document that allows the document to be assigned to a person. This property results from predefined security features of the valuable or security products, preferably from the security printing according to the invention.

[0016] Where the term "color impression" is used in the description and claims of this application, it is to be understood as the optical impression on a human observer with regard to the color effect. These different impressions can result from different color tones, i.e., spectrally different absorptions, and / or brightnesses of a print. The color impression can also result from interacting, closely spaced discrete color tones, which evoke a color impression in a human observer that differs from each of the closely spaced color tones. Where the term "dye" is used in the description and claims of this application, it is to be understood as a substance or a mixture of substances. The substance or substances exhibit light absorption in the visible spectral range.In contrast to a color pigment, they are chemically dissolved in a printing ink.

[0017] Where the term "color pigment" is used in the description and claims of this application, it refers to a substance or mixture of substances. This substance or these substances exhibit light absorption in the visible spectral range. Unlike a dye, they are chemically insoluble in a printing ink and are present therein in the form of separate particles.

[0018] Where the term "visual" is used in the description and claims of this application, it is understood to refer to the visual perception of a person with normal vision, particularly with regard to the spectrum of perceived wavelengths. "Visual" therefore refers to wavelengths in the visible spectrum. This includes the pure correction of a visual impairment, such as nearsightedness or farsightedness, without any measures that shift the light spectrum.

[0019] Claim 1 defines a method according to the invention for producing a document with a document body and a visually imperceptible security feature associated with the document body. This method comprises providing a key pair consisting of a public and private key, i.e., an asymmetric cryptographic key pair, and encrypting data unique to the document with the public key of the key pair. The use of a key pair consisting of a public and private key makes it possible to perform encryption at a variety of locations without the key required for decryption being available at these various locations. This makes it easier to keep the private key secret.

[0020] The method further comprises encoding the encrypted data into a graphic code, in particular an optoelectronically readable graphic code. The graphic code can be, for example, a one-dimensional code, such as a barcode, or a two-dimensional code, such as a matrix code, for example a QR code, which are composed of combinations of two distinguishable elements.

[0021] The method also includes providing a color photo to be associated with the document, such as a portrait of a person, a photo of an animal or an object to which the document refers, and embedding the graphic code in the color photo.

[0022] The method further comprises linking the photo and the graphic code embedded therein to the document body.

[0023] The photo and the graphic code embedded therein can be connected to the document body, for example, by printing on the document body, for example onto a carrier layer of the document body. The carrier layer is a layer that is intended as a carrier for the photo and the graphic code embedded therein or for printing with the photo and the embedded graphic code. The document body is, for example, a composite body that comprises a plurality of material layers. One of these material layers is, for example, the carrier layer. For example, the photo and the graphic code embedded therein are printed on one or more carrier layers. For example, the photo and the graphic code embedded therein are printed in regions distributed across several carrier layers.

[0024] In a widely used printing process, a multitude of color tones are printed with just a few printing inks to represent color images, for example by printing very small, closely spaced areas or dots with the colors cyan, magenta, yellow and black. These printing inks are also abbreviated to C, M, Y and K. Viewed from a distance at which the areas printed with a single color are no longer individually perceptible, these areas appear in a wide variety of color tones depending on the area ratio of the printing inks. In particular, the black printing ink, K, can exist in two different versions, K and K+, which are visually indistinguishable, one of which is transparent to IR light and the other opaque. Depending on the color tone, each area of ​​a color image has a greater or lesser proportion of black printing ink.When the graphic code is embedded in the photo, the black part of the color photo is printed with one version of the black ink in areas of the photo where the first of the two distinguishable elements of the graphic code are located, while in areas of the photo where the second of the two distinguishable elements of the graphic code are located, the black part of the color photo is printed with the other version of the black ink. Because the two versions are visually indistinguishable, a human observer sees a normal color photo. This visual indistinguishability also applies to images taken with a color camera, i.e. the signals from the color camera for the different versions of the printing inks are identical. When illuminated with IR light and taken with a camera sensitive to the IR spectrum, the graphic code becomes visible.In particular, the elements of the graphic code printed with the IR light-absorbing version of the black printing ink can have strongly fluctuating absorption levels within an element or from element to element, which depend on the image content of the color image.

[0025] This can be taken into account when generating the graphic code, for example, through suitable error correction measures (Forward Error Correction, FEC). Furthermore, a graphic code that does not take up the entire surface of the photo can be positioned at a point in the photo that has the smallest fluctuations in the proportion of black printing ink across the surface of the graphic code. It is sufficient if the fluctuations in the proportion of black printing ink are minimized in the areas printed with the IR-absorbing variant of the printing ink. The information about the black components can already be available when the photo is rendered into the individual printing colors or can be generated through appropriate analysis. The graphic code can then be positioned at different points within the image, and the respective fluctuations in the proportion of black printing ink can be determined.

[0026] The method of claim 1 comprises providing an assignment that depicts a relationship between color signals from a color camera and monochrome signals from a camera sensitive to the infrared spectrum (IR) for a plurality of color tones produced by mixing printing inks intended for the production of the document. The signals from the color camera are, for example, triplets of values ​​for the primary colors red, green, and blue (RGB) or signals derived therefrom, such as YP b P r or YC b C r . The monochrome signals from the camera sensitive to the IR spectrum correspond to brightness levels of the respective color tones when the color tones are illuminated with IR light. The relationship between the color signals and the monochrome signals can, for example, be in the form of a mapping table (LUT) or in the form of one or more analytical descriptions.

[0027] The relationship can be established, for example, by creating a color image of a color reference chart and a corresponding image with the camera sensitive in the IR spectrum when illuminated with light in the IR spectrum, whereby the signals of the color camera and the camera sensitive in the IR spectrum are assigned to each other for identical image areas in the images.

[0028] The assignment can, for example, map the relationship between the color signals and the monochrome signals for a carrier material, a printing process, and / or a surface coating used in the production of the document. Corresponding information about the parameters or materials underlying or used in the production process, and the corresponding assignment, can, for example, be attached to the document in machine-readable form or be determined by analyzing the document. The information can also be attached to the document as a reference, e.g., as a reference to an entry in a database. Based on the specific assignment, the placement of the graphic code in the photo can be adapted depending on its content and / or the recognition of the graphic code can be improved during inspection.

[0029] In an embodiment in which the document body has a plurality of layers arranged one above the other, connecting the photo and the graphic code embedded therein to the document body comprises printing the photo and the graphic code embedded therein onto one or more of the layers of the document body. Alternatively, adjacent areas of the photo and the graphic code embedded therein can be printed onto different layers of the document body in such a way that the boundaries of the adjacent areas are not recognizable when viewed perpendicular to the surface of the document body, but the viewer sees a complete image. The adjacent areas can have any shape, e.g.Rectangles or squares; however, it is also conceivable to print individual adjacent pixels composed of multiple printing inks on different layers of the document body, or individual printing inks in separate layers. The layers of the document body are then inseparably glued and / or fused together. Inseparably means, in particular, not separable without destruction. If layers of the document body are joined together inseparably or in a way that cannot be separated without destruction, for example by glueing and / or fusion, these layers can no longer be separated from one another in such a way that at least one of the layers is in its original state, i.e. its state before joining. After gluing and / or fusion, the printing inks are preferably located inside the document.During gluing or fusing, printing inks can penetrate into the document body and bond with it, so that even if the layers are removed layer by layer, a surface cannot be obtained at any time that shows the complete photo and the graphic code embedded in it.

[0030] By printing over several layers, it is possible to avoid the situation where some layers are first removed and then new layers containing incorrect information are applied to the rest of the original document body, without at least destroying the graphic code or making it unreadable.

[0031] In one or more embodiments, the method further comprises applying or affixing the data unique to the document to or on the document in at least one further representation. The at least one further representation may, for example, comprise an alphanumeric representation, in plain text or encrypted, a representation in a hologram, or the like.

[0032] This can provide a simple way to determine the authenticity of the document, or at least to determine that the document has not been tampered with, by comparing the data of the graphic code embedded in the photo with data extracted from the further representation.

[0033] In one or more embodiments, the method further comprises connecting an electronic circuit to the document body. The electronic circuit, e.g., a microchip with an interface for contact or contactless communication with the electronic circuit and a memory, can store a representation of the data unique to the document, which can be compared with data contained in the graphic code.

[0034] Alternatively or additionally, the electronic circuit can store additional data that is specially protected against unauthorized access. To access this data, the graphic code can contain access data that is fed to the electronic circuit during an authentication or authorization phase. The electronic circuit can, for example, be configured to compare the data from the graphic code with access data stored in the electronic circuit.

[0035] If the comparison shows that the access data matches, the electronic circuit can allow access to the other stored data. Accordingly, matching access data is stored in the graphic code and the electronic circuit during document creation.

[0036] The electronic circuit can be a semiconductor circuit, e.g., silicon-based or polymer electronic. For example, the electronic circuit can be implemented by a chip located on or in a document layer. The electronic circuit can also be formed from polymer electronic components, e.g., applied to the document layer by printing.

[0037] A method according to the invention for verifying a document produced according to one of the above-described embodiments of the method comprises taking a color image of at least the photo associated with the document with a color camera, and taking a monochrome image of the photo associated with the document with a camera sensitive in the IR spectrum under illumination with infrared light. The monochrome image corresponds to a brightness level image and can also be displayed as a grayscale image. The method further comprises calculating an image from the color image that corresponds to its brightness level image if it had been taken with a camera sensitive in the IR spectrum under illumination with infrared light. The calculation can be carried out using the mapping provided during the production of the document.When calculating the brightness level image, only one opaque variant of a printing ink available in two variants is taken into account, the other variant of which is transparent when illuminated with infrared light. Once the calculated image is available, it is compared with the monochrome image captured by the camera sensitive to the IR spectrum under IR light illumination. The comparison involves comparing the brightness levels of the calculated image and the monochrome image, with identical areas of the images being compared. An adjustment of the image brightness and / or contrast can be made for one or both images before the comparison. The comparison results in a difference image in which the graphic code embedded in the photo may already be recognizable.

[0038] In a further step of the method, the binary graphic code is reconstructed from the difference image. Coding parameters supplied to the device executing the method, which were used in generating the graphic code, can be used, for example, a number of adjacently arranged modules, their spatial extent, an error correction used in coding, and the like. The coding parameters can be supplied, for example, from a database. Information can be present on the document, which is supplied to the database in order to select the coding parameters appropriate for the document. This information is preferably designed to be machine-readable. The coding parameters can be transmitted to the device executing the method via a secure data connection. The reconstructed graphic code is then decoded.

[0039] As an alternative to local reconstruction, the difference image can be sent to a reconstruction device located remotely from the device performing the method, preferably via a secure data connection, wherein the reconstruction device returns the reconstructed graphic code or the decoded content of the graphic code to the device performing the method. The reconstruction device can also use coding parameters used in generating the graphic code for reconstruction. During reconstruction in a remote reconstruction device, the coding parameters do not need to be sent to multiple reading devices, which can contribute to improved security.

[0040] The content of the decoded graphic code, which is in encrypted form, is decrypted in a further step of the process using the private key associated with the public key used in the encryption.

[0041] The private key can be supplied to the device executing the method, preferably via a secure data line, wherein the key can be selected on the basis of preferably machine-readable information contained on or in the document.

[0042] As an alternative to local decryption, the encrypted information can be sent to a decryption device located remotely from the device executing the method, preferably via a secure data connection, with the decryption device returning the decrypted content to the device executing the method. When decrypting in a remote decryption device, the private key does not need to be sent to multiple reading devices, which can contribute to improved security.

[0043] The reconstruction device and the decryption device can be arranged together in a unit arranged remotely from the reading device, so that the reconstruction and the decryption are carried out in one go on the remotely arranged unit and only the decrypted content of the graphic code has to be sent back to the device executing the method, for example the reading device.

[0044] After decryption, the decrypted information is provided in a digitally processable format.

[0045] The method further comprises extracting data unique to the document from at least one further representation contained in the document, and providing the extracted data in a digitally processable format. Extracting the data unique to the document from at least one further representation can preferably be performed from an image of the region of the document containing the further representation, captured by the camera sensitive to the IR spectrum under infrared illumination.

[0046] The method also includes comparing the decrypted information with the data extracted from the further representation contained in the document and determining a degree of match. Once a specified degree of match is reached, the document is classified as authentic, and a corresponding signal is issued. This signal can, for example, be an authorization signal for access control, such as a security gate or the like.

[0047] A system for verifying a document produced according to one of the above-described embodiments of the method comprises a color camera, a light source whose light enables the color camera to capture a color image, a camera sensitive to the IR spectrum that generates a brightness-gradient image when an object is illuminated with infrared light, and an infrared light source for illuminating at least one area of ​​the document to be captured by the camera sensitive to the IR spectrum. The color camera and the camera sensitive to the IR spectrum can also be combined in one camera, e.g., if one camera outputs a color image when illuminated with essentially white light and a brightness-gradient image when illuminated with light lying essentially in the IR spectrum.

[0048] The system further comprises a first memory providing a mapping representing a relationship between color signals from a color camera (RGB) and monochrome signals from a camera sensitive to the IR spectrum for a plurality of color tones produced by mixing printing inks intended for the production of the document, the monochrome signals corresponding to brightness levels of the respective color tones when illuminated with IR light.

[0049] The system further comprises a conversion module which is configured to calculate an image from a color image recorded by the color camera using the assignment, which image corresponds to its brightness level image when recorded by a camera sensitive in the IR spectrum when illuminated with infrared light, if only one variant of a printing ink which is available in two variants and whose other variant is transparent when illuminated with infrared light is used.

[0050] In addition, the system comprises an extraction module which is configured to extract data unique to the document from at least one further representation contained on or in the document and to provide it in a digitally processable format, and a first comparison module which compares the brightness level image recorded under illumination with infrared light by the camera sensitive in the IR spectrum with the brightness level image calculated from the color image and forms a difference image which contains a graphic code.

[0051] The system also includes a second memory that provides coding parameters used in encoding encrypted data into the graphic code, and a reconstruction module configured to reconstruct the graphic code from the difference image using the provided coding parameters. The second memory can be arranged in a device with the reconstruction module or connected to the reconstruction module via a data connection. Furthermore, the system includes a decoder module or decoding module configured to decode the reconstructed graphic code and provide its content in a digitally processable format.

[0052] The system further comprises a third memory providing a private key of a key pair associated with a public key used in the encryption of the data contained in the graphical code, and a decryption module configured to decrypt the content of the decoded reconstructed graphical code with the provided private key and to provide the decrypted information in a digitally processable format.

[0053] The system further comprises a second comparison module configured to determine the degree of correspondence between the decrypted information and the data unique to the document extracted from the at least one further representation. The second comparison module is also configured to classify the document as authentic if the degree of correspondence exceeds a specified value and to output a corresponding signal.

[0054] The conversion module, the extraction module, the first and second comparison modules, the reconstruction module, the decoder module, and the decryption module can be implemented as computer programs or as hardware components, or as a combination of hardware components and computer programs. Several of the modules can be implemented in one computer or device; however, the modules can also be implemented in separate computers or devices that are communicatively connected to one another. The first, second, and third memories can be formed by databases that are part of the system or are communicatively connected to it. The system can have local memory assigned to one or more of the modules, which at least temporarily stores data obtained from the databases.

[0055] The system can be communicatively connected to an access control device, e.g. a security gate for goods or persons, wherein the signal output by the second comparison module is fed to the access control as an enable signal. Short description of the drawing

[0056] The invention is described below with reference to the drawing. Fig. 1 shows an exemplary flow diagram of an embodiment of the method according to the invention for producing a document with a document body and a visually imperceptible security feature connected to the document body, Fig. 2 shows an exemplary flow diagram of sub-steps of the method according to the invention for producing a document with a document body and a visually imperceptible security feature connected to the document body, Fig. 3 shows an exemplary flow diagram of a method according to the invention for verifying a document with a document body and a visually imperceptible security feature connected to the document body, Fig. 4 shows an exemplary block diagram of a system for verifying a document with a document body and a visually imperceptible security feature connected to the document body, Fig.Fig. 5 shows an exemplary embodiment of a variant of a document produced according to the method according to the invention, and Fig. 6 shows an exemplary example of a view of a document produced using the method described herein that would be presented to a human observer.

[0057] Identical or similar elements are provided with identical or similar reference numerals in the figures. Example

[0058] Figure 1shows an exemplary flowchart of an embodiment of the method 100 according to the invention for producing a document with a document body and a visually imperceptible security feature connected to the document body. In step 104, a key pair consisting of a public and private key is provided. With the public key of the key pair, data unique to the document is encrypted in step 106 and encoded into a graphic code, e.g., a barcode or a matrix code, in step 108. In step 110, a photo to be associated with the document is provided, into which the graphic code is embedded in step 112. For this purpose, an assignment is provided in step 102 that maps a relationship between color signals from a color camera and monochrome signals from a camera sensitive to the IR spectrum for a plurality of color tones generated by mixing printing inks intended for producing the document.The monochrome signals correspond to brightness levels of the respective color tones when illuminated with IR light. Finally, in step 114, the photo with the graphic code embedded therein is linked to the document body, e.g., by printing. Printing can be performed using one of two visually indistinguishable variants of one of the printing inks intended for the production of the document, one of which is opaque when illuminated with infrared light, the other transparent, and for which the color signals recorded by the color camera are indistinguishable. The respective variant of the printing ink, which is available in two variants, is selected when the graphic code is embedded in the photo in step 112 and fed to a printing device as printing information.

[0059] Figure 2shows an exemplary flowchart of substeps of the method 100 according to the invention for producing a document with a document body and a visually imperceptible security feature connected to the document body. The substeps relate to the provision of the assignment in step 102 of the method 100, more precisely to the creation of the assignment. In step 102-1, a color reference chart is first printed using the printing inks intended for the production of the document and, if applicable, a carrier material intended for the production of the document. The color reference chart depicts a plurality of color tones that occur in one or more photos to be associated with the document. In step 102-2, a color image of the color reference chart is recorded, and in step 102-3, a monochrome image is recorded using a camera sensitive in the IR spectrum while illuminating the color reference chart with IR light.Steps 102-2 and 102-3 can be performed in any order. In step 102-4, the color tones of the color image arranged at specific positions in the color reference table are assigned to brightness values ​​of the monochrome image located at corresponding positions. The assignment can be provided as a mapping table or in the form of an analytical description.

[0060] Figure 3shows an exemplary flowchart of a method 300 according to the invention for verifying a document having a document body and a visually imperceptible security feature associated with the document body. In step 302, a color image of at least one photo associated with the document 200 is captured with a color camera, and in step 304, a monochrome image of at least the photo associated with the document 200 is captured with a camera sensitive in the IR spectrum under illumination with IR light. The order of the captures is irrelevant. In step 306, an image is calculated from the color image that corresponds to its brightness level image when captured by a camera sensitive in the IR spectrum under illumination with infrared light, if only one opaque variant of a printing ink available in two variants is used, the other variant of which is transparent when illuminated with infrared light.For this purpose, an assignment can be provided in step 306-1, for example one in the with reference to . Figure 2described type of association. In step 308, the monochrome image is compared with the image calculated from the color image, and a difference image is formed. In step 310, a graphic code embedded in the photo is reconstructed from the difference image, the content of which is decoded in step 312. For this purpose, coding parameters supplied in step 310-1, which were used in generating the graphic code, can be used. The coding parameters can preferably be transmitted in encrypted form. Alternatively, the difference image can be transmitted in step 310-2 to a reconstruction device, which in step 310-3 sends back the reconstructed graphic code for decoding in step 312. Alternatively, the reconstruction device can also send back the decoded content so that it is immediately decrypted in step 314. The reconstruction device can be communicatively connected to the other components of the system.A reconstruction device can be connected to multiple subsystems, so that not every subsystem needs to have its own reconstruction device. In step 314, the decoded content of the graphical code is decrypted using the private key associated with the public key used in the encryption, and the decrypted information is provided in a digitally processable format. For decryption, the private key can be supplied in step 314-1. Alternatively, the decoded content can be transmitted in step 314-2 to a decryption device, from which the decrypted content is returned in step 314-3. In one variant, the decoded content can also be sent directly from the reconstruction device to the decryption device, from where the decrypted information is returned to the device executing the method.In step 316, data unique to the document is extracted from at least one other representation contained in the document and made available in a digitally processable format. The extraction can preferably be carried out from the monochrome image, but it is also possible to use the color image for the extraction. At which point in the process the extraction takes place is of secondary importance; what is important is that the data is available before step 318, in which the decrypted information is compared with the data extracted from the other representation contained in the document. In the subsequent step 320, a degree of match is determined. From a specified degree of match, the document is classified as authentic and a corresponding signal is output.

[0061] Figure 4shows an exemplary block diagram of a system 400 for verifying a document with a document body and a visually imperceptible security feature connected to the document body. The system includes a color camera 402 and a camera 406 sensitive to the IR spectrum, as well as a light source for color images 404 and an IR light source 408. The cameras 402, 406 capture images of the document 200, also shown in the figure and illuminated by the light sources 404, 408, which is not part of the system.The image from the color camera is sent to a conversion module 412, which calculates an image from the color image using an assignment supplied from memory 410. The image corresponds to the brightness level image recorded by an IR-sensitive camera under infrared light illumination, using only one opaque variant of a printing ink available in two variants, the other variant of which is transparent when illuminated with infrared light. The calculated image and the image from the IR-sensitive camera 406 are sent to a first comparison module 416, which compares the brightness level image recorded by the IR-sensitive camera 406 under infrared light illumination with the brightness level image calculated from the color image and forms a difference image containing a graphic code.The image from the IR-sensitive camera 406 is also fed to an extraction module 414, which is configured to extract data unique to the document from at least one further representation and to provide it in a digitally processable format. Alternatively or additionally, the color image can be fed to the extraction module 414. The difference image formed in the first comparison module 416 is fed to a reconstruction module 420, which is configured to reconstruct the graphic code from the difference image. To this end, the reconstruction module 420 can use coding parameters provided by a second memory 418 that were used during coding. The reconstructed graphic code is fed to a decoder module 422, which is configured to decode the reconstructed graphic code and provide its content in a digitally processable format.The decoded content is fed to a decryption module 426, which is configured to decrypt the content of the decoded, reconstructed graphic code and to provide the decrypted information in a digitally processable format. To this end, the decryption module 426 can use private keys of a key pair provided by a third memory 424, each associated with the public key. The decrypted information and the data extracted from the further representation are fed to a second comparison module 428, which is configured to determine a degree of correspondence between the decrypted information and the data unique to the document extracted from the at least one further representation.Furthermore, the second comparison module 428 is configured to classify the document 200 as authentic, valid, or the like if the degree of agreement exceeds a specified value and to output a corresponding signal. The signal can be sent, for example, to an access control device 430 to grant or deny a person access to a protected area depending on the result of the document verification.

[0062] Figure 5 shows an exemplary embodiment of a document 200 produced according to the method according to the invention when captured with a camera under illumination in the visible spectrum of light and when captured with a camera sensitive in the IR spectrum under illumination with IR light. In Figure 5the image is shown which appears to a human observer under appropriate lighting, ie the observer sees the photo 202 embedded in the document. In a document produced according to the method according to the invention, a camera sensitive to the IR spectrum will take an image under illumination with IR light, as shown in Figure 5 is depicted, ie, a security feature 208 embedded in the image is recognizable. In a document 200 not produced according to the method according to the invention, however, only the part of the photo 202 formed by the IR-light absorbing black color particles would be recognizable, shown in Figure 5 .

[0063] Figure 5shows an exemplary embodiment of a variant of a document 200 produced according to the method according to the invention. The document body of the document shown in the figure comprises four layers 200-1, 200-2, 200-3, and 200-4, which are inseparably connected to one another to obtain the document 200. A portion of a photograph 202 with a visually imperceptible security feature 208 embedded therein, or a portion thereof, can be connected to each of the layers 200-1, 200-2, 200-3, and 200-4. Only in the connection are all parts of the photograph and the security feature 208 embedded therein arranged together in such a way that a viewer can recognize the photograph, and a camera sensitive to the IR spectrum can completely record the security feature 208 when illuminated with IR light.In the figure, the photo with the security feature 208 embedded in it is shown as a monochrome image from the camera sensitive to the IR spectrum for reasons of clarity - a human observer would not perceive the matrix code representing the security feature 208.

[0064] Additionally, a further feature, such as a serial number 204, may be provided, the individual digits or possibly letters or other characters of which are each printed once on different layers of the document body, so that the complete serial number is only obtained when all layers are combined to form the finished document. Also connected to layer 200-2 is an electronic circuit 206, which has an interface for contact or contactless communication with a reader not shown in the figure. For the sake of clarity, further contents of the document are not shown in the figure. Figure 6 shown.

[0065] Figure 6 shows another example of a view of an exemplary document 200 produced by the method described herein that would be presented to a human observer, with additional features not described in detail here. List of reference symbols 100 Manufacturing process 310-1 Provide coding parameters 102 Provide 310-2 Diff. image on reconstruction device 102-1 Press 310-3 Returning the reconstructed code 102-2 Take a color picture 312 Decoding 102-3 Take a monochrome picture 314 Decrypt 102-4 Assign 314-1 Receiving private keys 104 Provide 314-2 encrypted message to decryption device 106 Encrypt 314-3 Receiving decrypted content 108 Coding 316 Extracting data from further representation 110 Provide 318 Comparison of decrypted content & extracted data 112 Embed 320 Determine the degree of agreement 114 Connect 400 Test system 200 document 402 Color camera 200-1 first layer 404 light source 200-2 second layer 406 camera sensitive to the IR spectrum 200-3 third layer 408 IR light source 200-4 fourth layer 410 first memory 202 photo 412 Conversion module 204 Serial number 414 Extraction module 206 electronic circuit 416 first comparison module 208 Security feature 418 second storage 300 Test procedures 420 Reconstruction module 302 Color image recording 422 Decoder module 304 Monochrome image recording 424 third storage 306 Calculate brightness level image 426 Decryption module 306-1 Assignment provision 428 second comparison module 308 Difference image generation 430 Access control device 310 Code reconstruction

Claims

1. A method (100) for producing a document (200) having a document body and a visually imperceptible security feature joined to the document body, said method comprising: - providing (104) a key pair formed of public and private key, - encrypting (106) data unique for the document using the public key of the key pair, - encoding (108) the encrypted data into a graphical code as the security feature, - providing (110) a photo to be joined to the document, - embedding (112) the graphical code in the photo, and - joining (114) the photo and the graphical code embedded therein to the document body, the method additionally comprising: - providing (102) an assignment that portrays a relationship between colour signals of a colour camera (402) and monochrome signals of a camera (406) sensitive to the IR spectrum for a variety of colour tones created by mixing printing inks provided to produce the document, wherein the monochrome signals correspond to brightness levels of the respective colour tones when illuminated with IR light, and - applying, to the document, information relating to the assignment or a reference referring to the assignment.

2. The method (100) according to claim 1, wherein the assignment portrays the relationship between the colour signals and the monochrome signals for a carrier material used in the production of the document, a printing process and / or a surface coating, and / or wherein the coding (108) comprises the generation of a barcode or matrix code.

3. The method (100) according to any one of claims 1-2, wherein the joining (114) of the photo and of the graphical code embedded therein to the document body comprises: - printing the photo and the graphical code embedded therein onto a carrier layer of the document body.

4. The method (100) according to claim 3, wherein the embedding (112) of the graphical code in the photo comprises: - selecting one of two visually indistinguishable variants of one of the printing inks provided for the production of the document, one variant of which is opaque when illuminated with infrared light and the other variant of which is transparent when illuminated with infrared light, and for which the colour signals recorded by the colour camera are the same.

5. The method (100) according to claim 4, wherein the graphical code occupies an area that is smaller than the area of the photo, the method additionally comprising: - determining an area within the photo having the outer dimensions of the graphical code, within which the smallest fluctuations in the proportion of the printing ink present in two variants occur, and - embedding the graphical code within the determined area.

6. The method (6) according to any one of claims 4-5, wherein the document body has a plurality of layers arranged one above the other, the method additionally comprising: - printing the photo and the graphical code embedded therein onto one or more of the layers, or - printing adjoining regions of the photo and of the graphical code embedded therein onto different layers, wherein the boundaries of the adjoining regions are not perceptible when viewed perpendicular to the surface of the document body, and - inseparably bonding and / or fusing the layers.

7. The method (100) according to claim 6, wherein dyes or colour pigments of the printing inks penetrate the material of at least one of the layers during the bonding or fusing process.

8. The method (100) according to any one or more of the preceding claims, wherein the data unique for the document (200) are contained in at least one further representation in or on the document (200), and / or the method additionally comprising: - joining an electronic circuit (206) to the document body, wherein the electronic circuit (206) stores a representation of the data unique for the document (200), and / or wherein the electronic circuit (206) stores further data, which may only be accessed following successful authentication and / or authorisation.

9. A method (300) for checking a document (200) that has been produced in accordance with any one of claims 1 to 8, the method comprising: - recording (302), using a colour camera (402), a colour image of at least one photo joined to the document (200), - recording (304), using a camera (406) sensitive in the IR spectrum and under illumination with infrared light, a monochrome image of the photo joined to the document (200), - calculating (306) an image from the colour image that corresponds to its brightness level image when recorded by a camera sensitive in the IR spectrum under illumination with infrared light when only an opaque variant of a printing ink present in two variants is used, the other variant of which is transparent under illumination with infrared light, - comparing (308) the monochrome image, recorded under illumination with infrared light, from the camera (406) sensitive in the IR spectrum with the image calculated from the colour image, and forming a difference image, - reconstructing (310) a graphical code, embedded in the photo, from the difference image and decoding (312) its content, - decrypting (314) the decoded content contained in the graphical code with the aid of the private key belonging to the public key used for the encryption, and providing the decrypted information in a digitally processable format, - extracting (316) unique data for the document from at least one further representation contained in the document, and providing the extracted data in a digitally processable format, - comparing (318) the decrypted information with the data extracted from the further representation contained in the document, and determining (320) a degree of conformity, wherein the document is classified as genuine from a defined degree of conformity and a corresponding signal is emitted.

10. The method (300) according to claim 9, wherein the reconstruction (310) of the binary graphical code embedded in the photo from the difference image additionally comprises: - supplying (310-1) coding parameters which were used in the generation of the graphical code, or - transmitting (310-2) the difference image to a remotely arranged reconstruction device, and - receiving (310-3) the decoded content of the graphical code from the reconstruction device.

11. The method (300) according to claim 9 or 10, wherein the decryption (314) of the decoded content contained in the graphical code additionally comprises: - supplying (314-1) the private key belonging to the public key used in the encryption, or - transmitting (314-2) the encrypted information to a decryption device arranged remotely from the device carrying out the method, and - receiving (314-3) the decrypted content of the graphical code from the decryption device.

12. The method (300) according to claim 9, 10 or 11, wherein the extraction (316) of the data unique for the document is performed from at least one further representation from the monochrome image, recorded by the camera sensitive in the IR spectrum and under illumination with infrared light, of the region of the document containing the further representation.

13. A system (400) for checking a document produced in accordance with any one of claims 1 to 8, the system comprising: - a colour camera (402), - a light source (404) for the colour camera (402), the light of which makes it possible to record a colour image by the colour camera (402), - a camera (406) sensitive in the IR spectrum, which generates a brightness level image or monochrome image when an object is illuminated with infrared light, - an infrared light source (408) for illuminating at least one region of the document to be recorded by the camera (406) sensitive in the IR spectrum, - a first memory (410), which provides an assignment that portrays a relationship between colour signals of a colour camera (402) and monochrome signals of a camera (406) sensitive to the IR spectrum for a variety of colour tones created by mixing printing inks provided to produce the document, wherein the monochrome signals correspond to brightness levels of the respective colour tones when illuminated with IR light, - a recalculation module (412), which is set up to calculate from a colour image, with use of the assignment, an image that corresponds to its brightness level image when recorded by a camera sensitive in the IR spectrum under illumination with infrared light when only an opaque variant of a printing ink present in two variants is used, the other variant of which is transparent under illumination with infrared light, - an extraction module (414), which is set up to extract data unique for the document from at least one further representation and to provide it in a digitally processable format, - a first comparison module (416), which compares the brightness level image of the camera (406) sensitive in the IR spectrum, recorded under illumination with infrared light, with the brightness level image calculated from the colour image and forms a difference image containing a graphical code, - a second memory (418), which provides coding parameters used in the coding of encrypted data into the graphical code, - a reconstruction module (420), which is set up to reconstruct the graphical code from the difference image with the help of the provided coding parameters, - a decoding module (422), which is set up to decode the reconstructed graphical code and to provide its content in a digitally processable format, - a third memory (424), which provides a private key of a key pair belonging to a public key used for the encryption of the data contained in the graphical code, - a decryption module (426), which is set up to decrypt the content of the decoded reconstructed graphical code with the provided private key, and to provide the decrypted information in a digitally processable format, - a second comparison module (428), which is set up to determine a degree of conformity between the decrypted information and the data, unique for the document, extracted from the at least one further representation, wherein the second comparison module (428) is additionally set up to classify the document as genuine if the degree of conformity exceeds a defined value and to emit a corresponding signal.

14. The system (400) according to claim 13, wherein, in the event of a positive checking result, a signal emitted by the second comparison module is suppled as a release signal to actuate an access control device (430).

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