SECURITY DOCUMENT, METHOD FOR ITS PRODUCTION, ELECTRONIC PRINTING SYSTEM AND READER

Description

[0001] The present invention relates to a security document with a colored print, a method for producing a security document, an electronic printing system and a reading device.

[0002] Various valuable and security documents as well as devices and methods for verifying the authenticity of valuable or security documents are known from the state of the art.

[0003] From DE 38 407 29 A1, for example, a multi-layer recording medium, in particular an identity card, is known in which an outer color layer has a first color and an inner color layer has a second color.

[0004] Color printing is based on subtractive color mixing and serves as a precursor to the printing process. Color separation refers to the calculation of individual printing colors in prepress. In four-color printing, the three transparent printing colors cyan (C), magenta (M), and yellow (Y), as well as black (K), are used. The black (K) is necessary because 100% application of cyan, magenta, and yellow does not produce true black, but only a dark brown. These four primary colors, which make up the so-called CMYK color model, are mixed and create many other colors using subtractive color synthesis. The print data for a document, for example, is usually in RGB (red, green, blue) and must be converted to CMYK for printing. The conversion process from RGB to CMYK is called color separation. It takes place either in the printer or is performed in an image editing program before printing (seeSee also "4 Colors 1 Image," Basics of Color Image Processing with Photoshop and QuarkXPress. 2nd edition, Edition Page by Mattias Nyman, published by Springer; especially page 12.

[0005] Color Printing. Effects, Representation, and Management of Digital Colors. Bertram Störch, published by Addison-Wesley. Digital Color Management: Colors in Publishing Practice. 2nd edition. Jan-Peter Homann, published by Springer; especially page 82.

[0006] Currently, every color printing system is based on the standardized 4C color model, as every color printer requires these four colors for printing. This means that the "color" data is converted to the CMYK color model before printing. Information such as personalization data (portrait, signature, or text) is converted from the original color space, e.g., RGB, into the CMYK color space. This color separation is usually performed automatically by the printer driver. Currently, IR-transparent cyan, magenta, yellow, and IR-visible black or UV-visible black are used for security printing. However, existing solutions are only partially suitable for security and specialty document printing, where other inks are used.

[0007] EP 2 953 059 B1 discloses a dot code arranged in a display matrix. The dot code creates a graphic indicator that can be recognized by an image processing method.

[0008] WO 2011 / 020537 A1 discloses an identification document provided with two superimposed images, as well as a method for producing such an identification document. Furthermore, the invention relates to a method for verifying the authenticity of such an identification document. In order to better protect such identification documents provided with a color image against forgery or manipulation, it is proposed that the images be applied in separate steps, that at least one of the images be in a form that is not accessible from the outside, that one of the images be a grayscale image, and that one of the images be a color image that includes both color information and light / dark information.

[0009] DE 10 2016 005415 A1 discloses a security element for protecting security papers, valuable documents, and other data storage media, comprising a luminescent print that displays a multicolored motif under UV light. According to the invention, the luminescent print is formed by luminescent white on the one hand and at least two luminescent primary dyes, in particular from the group consisting of luminescent green, luminescent red, and luminescent blue, on the other hand. The multicolored motif also contains achromatic components in colored areas, which are at least partially formed by luminescent white in the print.

[0010] DE10 2008 012425 A1 discloses a printing device and a method for producing preferably individualized security and / or valuable printed items. For this purpose, a digital printing device is used that prints at least one first ink formulation and at least one second ink formulation, which, when printed, have at least one physical distinguishing feature. The first and second ink formulations are printed in such a way that first and second print information are stored on the printed item, so that a human observer of the printed item, upon visual inspection, perceives the print information exclusively in the manner that would result from printing without the use of the at least second ink formulation, and the second print information is perceptible upon evaluation of the printed item using the at least one physical distinguishing feature.

[0011] US 2010 / 150433 A1 relates to the protection of documents. It applies, in particular, to a method for inserting variable data into documents that becomes visible when the document is copied.

[0012] From DE 44 17 343 A1 an identity card is known, in particular a credit card, with an image part containing a photo of the person to be identified, wherein pixels of different absorption are introduced point by point with a laser beam into a cover layer and / or into an intermediate and / or inlay layer located under a transparent cover layer.

[0013] DE 10 2012 211767 A1 generally relates to the field of producing security documents, security document blanks, and a method for subsequent personalization of security document blanks. In particular, the invention relates to a method for producing security document blanks intended for subsequent decentralized color personalization, such security document blanks, and a method for color personalization.

[0014] US 2016 / 214396 A1 discloses a printing system for printing a security feature with a single colorant that is substantially imperceptible to the naked human eye. A digital security image containing the security feature has a first region formed by a first pattern of binary pixels and an adjacent second region formed by a different second pattern of binary pixels. The first and second regions each have a similar gray value. The first and second patterns are printed on a printing medium with the single colorant.

[0015] The invention is therefore based on the object of creating an improved security document, a method for producing a security document, an electronic printing system and a reading device of the type mentioned at the outset.

[0016] The problem underlying the invention is solved by the features of the independent patent claim. Advantageous embodiments of the invention are specified in the dependent patent claims.

[0017] According to a preferred embodiment of the invention, a security document is created with a colored print, wherein a first part of the print comprises colored pigments, and in the first part of the print, the visual impression of an achromatic color is approximated by the colored pigments. A second part of the print comprises, in addition to the colored pigments, also achromatic pigments of the achromatic color. A "colored print" is understood here to include a print that is printed using color printing but only contains grayscale values, analogous to the reproduction of a black-and-white image on a color television. The visual perception of a "colored print" may, but does not necessarily, always create a color impression.

[0018] According to the invention, a document is understood to mean, among other things, paper-based and / or plastic-based documents, such as identification documents, in particular passports, identity cards, visas, driving licenses, vehicle registration documents, vehicle registration documents, company ID cards, health cards or other ID documents, as well as chip cards, means of payment, in particular bank cards and credit cards, waybills or other proof of authorization.

[0019] According to a preferred embodiment of the invention, the imprint on the security document provides an optical security feature. This has the advantage of making the document forgery-proof.

[0020] According to a further preferred embodiment of the invention, personalization information is provided on the security document by means of the imprint. This advantageously secures the document's personalization information.

[0021] According to a preferred embodiment of the invention, the achromatic ink in the security document has a sensory-detectable property. According to a further preferred embodiment of the invention, the sensory-detectable property integrated into the security document is an optical, magnetic, dielectric, and / or resistive property. For example, the achromatic ink contains particles whose optical, magnetic, dielectric, and / or resistive properties can be sensed by one or more sensors.

[0022] According to a preferred embodiment of the invention, the achromatic ink integrated into the security document is an ink containing particles that produce IR-visible black or UV-visible black in the print. The machine-readable information in the security document is a code for use in a cryptographic method, a cryptographic key or part of a cryptographic key, an identifier, an attribute, a seed value for a cryptographic method, and / or a cryptographic certificate or part of a cryptographic certificate.

[0023] According to a preferred embodiment of the invention, machine-readable information is provided in the security document by dividing the print into a first and a second part. This can be advantageous in making a forgery more visible and / or concealing the information.

[0024] According to a further preferred embodiment of the invention, a barcode, a QR code or a digital watermark with the machine-readable information is provided in the security document by dividing the print into the first and the second part.

[0025] According to a preferred embodiment of the invention, the division in the security document is carried out pixel by pixel. This advantageously creates high print quality, which advantageously makes any forgery of a document quickly detectable.

[0026] According to a further preferred embodiment of the invention, the division in the security document is uncorrelated with a visually perceptible geometric structure of the print. This means that there is no connection between the features, thus advantageously making the forgery of a document more difficult.

[0027] According to a further preferred embodiment of the invention, the security document includes an integrated electronic circuit and a memory for storing sensitive data and means for executing a cryptographic protocol. Furthermore, there is an interface to a reader.

[0028] According to a further preferred embodiment of the invention, a reader is provided with a sensor for detecting an imprint. A processor executes the program instructions.

[0029] According to one embodiment of the invention, the document is a valuable or security document, in particular a paper-based and / or plastic-based document, such as an identification document, in particular a machine-readable travel document (MRTD), in particular a passport, identity card, visa, driving license, vehicle registration document, vehicle registration document, company ID, health card or other ID document, a chip card, means of payment, in particular a bank card, credit card or an electronic means of payment, a waybill or other proof of authorization.

[0030] To carry out the method, an electronic printing system is configured, wherein the printing system includes the ability to transmit and receive images to and from a computer system via a network, and the computer system performs the steps of first and second color separation, selection and replacement of the image elements, and storage of the resulting image matrix.

[0031] According to a preferred embodiment, the printer is an inkjet printer that uses three different colored inks with colored pigments and one ink with achromatic pigments. Alternatively, a laser printer or thermal sublimation printer can be used.

[0032] According to a further preferred embodiment, the selection of the pixels of the second image matrix is ​​carried out as a function of information which is modulated onto the printout by replacing the pixels of the first image matrix.

[0033] Embodiments of the invention are particularly advantageous because the image pixels themselves carry the additional information and overlaying the image with a dot code that does not carry image information is not required.

[0034] Embodiments of the invention will be explained in more detail below with reference to the drawings. They show: Fig. 1 a block diagram of an embodiment of a security document according to the invention, Fig. 2 a block diagram of another embodiment of a security document according to the invention and a reading device, and Fig. 3 a block diagram of the method for producing a security document according to the invention.

[0035] The Fig. 1shows a security document 100 with a color separation using the example of a portrait with a sample personalization. Color separation means that individual, i.e. separated, printing colors are calculated in the prepress stage. In other words, a separation of the color information is performed. In this process, the print motif is broken down into its individual printing colors. This separation of the printing colors is described in the Fig. 1 shown. Colors are broken down into their four basic components: cyan, magenta, yellow, and black, according to the process color principle. Color separation is necessary because color information is usually not available in the form required for printing. Printing, preferably four-color printing, is usually done using the CMYK color model, which means a color mixture of the individual colors cyan, magenta, yellow, and black.

[0036] The Figure 1ashows a document blank 101 of a valuable or security document. The document blank 101 is card-shaped here, but can also have a different shape. The document blank 101 is intended to be printed with a colored imprint 104 of a passport photo as well as with textual information in black. The corresponding image data 102 of the passport photo can, for example, originally be present in the RGB color space and are transformed by a first color separation into a number of color channels, here for example cyan, magenta, yellow of the CMY color space, so that a first image matrix results. In an analogous manner, the image data 102 can be transformed by a second color separation into the same number of color channels and an additional achromatic channel, which in the embodiment considered here are cyan, magenta, yellow and the achromatic channel black, as in the Figure 1b shown.

[0037] From the resulting second image matrix with the achromatic channel, a part 112 is then selected, which in the example considered here is D-shaped, as in the Figure 1a This part 112 is then used to represent pixels of the CMY image matrix of the Figure 1a to replace. The resulting image matrix is ​​then saved as a raster graphics file, and the document blank 101 is printed by a printer that can process such a raster graphics file, so that the printer does not have to perform its own color separation for printing, as this is already stored as part of the raster graphics file. This results in the imprint 104 on the document blank 101; furthermore, the textual information is also printed by the printer.

[0038] Depending on the embodiment, the division of the colored print 104 into the two parts with or without achromatic pigments may or may not be visible to the naked eye.

[0039] According to one embodiment of the invention, the achromatic color comprises IR-visible black. If the security document 100 is illuminated with an IR radiation source 103, this results in only the achromatic portion of the print appearing, as shown in the Figure 1a In the embodiment shown here, only the D-shaped area and the textual information appear from the colored print 104.

[0040] Instead of a geometric area, such as the D-shaped area of ​​the Figure 1a and 1d, a different selection of pixels can also be made, for example to incorporate cryptographic information, such as a cryptographic key, into the print.

[0041] As in the Figure 1cFor example, instead of the D-shaped area, a selection of pixels from the CMYK image matrix can be made that encodes such information. A portion 112 formed in this way may or may not be visually perceptible in the resulting print 104, depending on the embodiment.

[0042] According to embodiments of the invention, a reader is required to detect the distribution of pixels of part 112 in the colored print 104. The reader can have an IR radiation source 103 for optically detecting part 112, e.g., if the achromatic color is IR-visible black.

[0043] Since the representations of black in the CMY and CMYK parts of the print are different, illumination in the visible spectral range can also be sufficient to detect the differences, for example with a CCD sensor or even with the naked eye.

[0044] According to further embodiments of the invention, the achromatic color has particles, in particular color particles, with other optical properties, such as UV-visible black, or other physically detectable properties, such as magnetic, dielectric and / or resistive properties, which can be detected by the reading device.

[0045] The security document 100 in Fig. 1thus shows a colored print 104. A first part of the print 110 has colored pigments 114, and in the first part of the print 110, the visual impression of an achromatic color is approximated by the colored pigments 114. A second part of the print 112, in addition to the colored pigments 114, also has achromatic pigments 116 of the achromatic color. This means that the print 104 is preferably divided into different areas, which can be printed with or without the use of achromatic pigments 116. The print 104 provides an optical security feature and personalization information.

[0046] Achromatic color means that the color has neither a specific hue nor a specific saturation, i.e., it is black, gray, or white. The achromatic color has a sensory-detectable property. This sensory-detectable property is an optical, magnetic, dielectric, and / or resistive property. This has the advantage that the detection of the achromatic color can be carried out using several physical measurement methods.

[0047] By dividing the print 104 into the first part 110 and the second part 112, machine-readable information can be provided, see in particular Fig. 1CThe machine-readable information is a code for use in a cryptographic procedure, a cryptographic key or part of a cryptographic key, an identifier, an attribute, a seed value for a cryptographic procedure and / or a cryptographic certificate or part of a cryptographic certificate.

[0048] By dividing the print 104 pixel-by-pixel into the first part 110 and the second part 112, a barcode, a QR code, or a digital watermark with the machine-readable information is created. By combining the information stored in the color and achromatic separation with the machine-readable area (MRZ), a key for unlocking the RFID chip can be obtained. The existing key from the MRZ is preferably combined with the stored information to advantageously generate a new, secure key. In other words, the stored information is generated by distinguishing between the first part of the print 110, in which black is used, and the second part of the print 112, in which no black is used. A type of fading is preferably performed between the first part of the print 110 and the second part of the print 112.This can preferably be done continuously or discontinuously. If it is done continuously, less black is used when printing each pixel between the first part of the print 110 and the second part of the print 112. In a discontinuous variant, areas of the image are alternately printed with and without black between the first part of the print 110 and the second part of the print 112. These areas can preferably be chosen to be as small as desired, for example, the size of a pixel. The fading advantageously brings about a smooth transition of a contrast difference between the first part of the print 110 and the second part of the print 112. This advantageously makes it more difficult for the forger to forge the document, since detecting and replicating the fading is difficult.

[0049] Fig. 1This demonstrates subtractive color theory by specifically utilizing the chromatic and achromatic separation of the CMYK channels to store machine-readable information in images. This has the advantage that, in the event of a falsification, the image to be falsified is further protected by the different channels, and any falsification becomes more visible.

[0050] In subtractive color theory, light of different colors is filtered out by color filters or absorbed by pigments. The remaining light forms a mixed color. In other words, color separation occurs with hidden background information, which is advantageous for ensuring document personalization. The primary colors of subtractive color theory are yellow, magenta, and cyan. Color separation is implemented using a printing system capable of printing the colors cyan, magenta, and yellow in such a way that a black that is as similar as possible is produced. This has the advantage that the additional information is not immediately apparent upon simple viewing without aids.

[0051] In the present invention, IR-transparent cyan, magenta, yellow, and an IR-visible black, or in other embodiments, a UV-visible black, are used for color separation. This means that the theory of subtractive color separation is utilized in such a way that the black channel is used as a mask for a security document 100, and the other colors are separated such that they create the same impression even without black. When an IR- or UV-visible black ink is used, only this information is visible, e.g., text / image, a number, or even a barcode. CMYK color separation has the advantage of making document falsification more difficult or even impossible. In addition, depending on the design of the inks, machine-readable information is possible in the IR or UV range.

[0052] The invention is particularly advantageous because in the case of a total forgery, the forger must separate the image accordingly using software and, in addition, the printing software and the corresponding inks must be available in order to be able to produce this print.

[0053] The Fig. 2 shows a further embodiment of the security document 100 according to the invention and a reader 132 using a block diagram. The security document 100 includes an integrated electronic circuit 106 and a memory 126 for storing sensitive data 127 and means for executing a cryptographic protocol 122. Furthermore, there is an interface 130 to a reader 132, wherein access by the reader 132 to the sensitive data 127 via the interface 132 requires the execution of the cryptographic protocol 132 using the machine-readable information.

[0054] The electronic circuit 106 contains one or more electronic memories 126 for storing, in particular, data 127. The electronic circuit 106 can access the data 127. In particular, the electronic circuit 106 serves to access the data 127 in order to control a display 108 for reproducing the data 127 so that a user of the security document 100 can visually perceive the reproduction of the data 127. The data 127 can be, for example, image data 102. Image data 102 here is understood to mean data 127 that is suitable for reproduction on the display, e.g., a digital photograph, textual information, a one- or two-dimensional barcode, or the like. The electronic circuit 106 is designed such that, during one refresh period, all of the display elements of the display 108 are controlled once in order to reproduce the data 127 on the display 108.This can be done with a refresh rate of, for example, 25 Hz or 50 Hz.

[0055] A cryptographic key is acquired by a reader 132, allowing the reader 132 to execute a cryptographic protocol 138 together with the security document 100. The cryptographic key can be a symmetric or asymmetric key. A condition for the reader 132 to access the additional data 127 is the prior successful execution of the cryptographic protocol 138. The cryptographic protocol 138 can, for example, be a so-called challenge-response method. The cryptographic protocol 138 protects the additional data 127 against unauthorized access. This is particularly advantageous when the third data is sensitive data, such as biometric data, in particular fingerprint data or iris scan data of the bearer of the security document 100.

[0056] The reader 132 has means for executing the cryptographic protocol 138 using the derived information 118. This information 118 is, for example, a cryptographic key. Based on the detection of the cryptographic key, the reader 132 can execute the cryptographic protocol 138 with the security document 100. After successfully executing the cryptographic protocol 138, the reader 132 can access a protected memory area of ​​the security document 100 to read data 127 from there.

[0057] The electronic circuit 106 of the security document 100 is embodied here as a chip, in particular as an RFID chip. The electronic circuit 106 is connected to an interface 130 of the security document 100 for communication with the reader 132. The interface 130 can, for example, have one or more antenna windings that run in an edge region of the security document 100. The security document 100 has a first colored print 110 with colored pigments 114 and a second colored print 112, which, in addition to the colored pigments 114, also has achromatic pigments 116 of the achromatic color.

[0058] The electronic circuit 106 has an electronic memory 126 for storing sensitive data 127. The sensitive data 127 can be, for example, biometric data of the bearer of the security document 100, such as fingerprint data, iris scan data, or the like. The sensitive data 127 is stored in a specially protected memory area of ​​the memory 126.

[0059] Furthermore, the data 127 and the information 118 are stored in the same memory 126 or another electronic memory of the security document 100. The colors of the data 127, in particular the colors of the image data 102, are as in the Fig. 1described separated data. The electronic circuit 106 further has a processor 128 for executing program instructions that implement the steps of a cryptographic protocol 122 relating to the security document 100. The processor 128 also serves to execute program instructions that implement a control program 120.

[0060] The electronic circuit 106 of the security document 100 is embodied here as a chip, in particular as an RFID chip. The electronic circuit 106 includes a driver circuit for controlling the display 108. For this purpose, the driver circuit includes a driver logic. The driver circuit and the driver logic are in the Fig. 2 not visible.

[0061] The electronic circuit 106 further has a processor 128 for executing program instructions that implement a control program 120, as well as for executing program instructions that serve to decode 124 the data 127. This decoding 124 is also referred to as "rendering." For example, the data 127 is encoded in a standardized data format, e.g., in JPEG, GIF, or TIFF format. The data 106 can be decoded using the program instructions 131.

[0062] The reader 132 has an optical sensor 146 for detecting an imprint 104 on a security document 100, with a colored imprint (104), wherein a first part of the imprint (110) comprises colored pigments (114) and, in the first part of the imprint (110), the visual impression of an achromatic color is approximated by the colored pigments (114), and wherein a second part of the imprint (112) comprises, in addition to the colored pigments (114), also achromatic pigments (116) of the achromatic color. The optical sensor 146 can be a CCD sensor or a scanner. The reader 132 further has an interface 140 that corresponds to the interface 130 of the security document 100. For example, the interface 140 is designed for RFID communication with the security document 100 or its circuit 106. The interfaces 130, 140 can be contact-based, contactless or designed as a so-called dual-mode interface.The interfaces 130, 140 can be based on an electrical, capacitive, inductive, magnetic, optical, or other physical coupling method. For contactless coupling via an antenna, this can be designed, for example, as a coil, dipole, or in the form of capacitive surfaces.

[0063] The security document 100 has at least one processor 128 for executing a control program 120 and program instructions by which steps of the cryptographic protocol 138 relating to the reader 132 are implemented. The reader 132 can further serve to execute an application program 144. The application program 144 can also be executed by another computer system connected to the reader 132.

[0064] By executing the program instructions, the reader 132 detects the positions of achromatic pigments 116 received from the security document 100 in an imprint 104 detected by the optical sensor 146. By executing the program instructions, information 118 is derived from the detected positions.

[0065] The security document 100 then transmits the data 127 requested by the reader 132 from the memory 126 from the interface 130 to the interface 140. This data 127 can be transmitted by the control program 120 to the application program 144 for further processing. For example, the data 127 is displayed on a screen.

[0066] Before the data 127 is transferred from the memory 126 to the reader 132, further checks may be required, such as an EAC procedure. Alternatively or additionally, a cryptographic protocol 122 based on an asymmetric key may also be used.

[0067] The electronic circuit 106 includes one or more electronic memories 126 for storing, in particular, data 127. The electronic circuit 106 can access the data 127. In particular, the electronic circuit 106 serves to access the data 127 in order to control the display 108 to display the data 127, so that a user of the security document 100 can visually perceive the display of the data 127.

[0068] Fig. 3shows a block diagram of a method for producing a security document 100 according to the invention, with a colored imprint 104, wherein a first part of the imprint 110 has colored pigments 114 and in the first part of the imprint 110 the visual impression of an achromatic color is approximated by the colored pigments 114, and wherein a second part of the imprint 112 has, in addition to the colored pigments 114, also achromatic pigments 116 of the achromatic color. First, a document blank and an image are provided, 302. The color of the image is subjected to a first separation into a number of color channels, resulting in a first image matrix, 304. After the first color separation, a second color separation of the image into the number of color channels is performed. There is a difference here, namely that an additional achromatic channel is provided, resulting in a second image matrix, 306.

[0069] Next, a selection of pixels from the second image matrix is ​​made, 308. Following this, the pixels from the first image matrix are replaced by the respective selected pixels from the second image matrix. The spatial arrangement of the pixels in the first image matrix corresponds to the selected pixels from the second image matrix. The selection of the pixels from the second image matrix is ​​dependent on information that is modulated onto the printout by replacing the pixels from the first image matrix, 310. The resulting image matrix is ​​saved as a raster graphics file, 312. Finally, the raster graphics file is printed onto the document blank using a printer, 314. The printer is an inkjet printer that uses three different colored inks with colored pigments and one ink with achromatic pigments.A raster graphic is also called a pixel graphic because it consists of individual image points, or pixels, that can have different colors. Raster graphics are a way of describing an image in the form of computer-readable data. The new image is preferably saved in CMYK color mode, e.g., TIFF format, and the separation is preferably saved in the profile.

[0070] The image is preferably transmitted to a computer system via a network, and the computer system receives or generates the information. The computer system carries out the steps of first and second color separation, the selection and replacement of the image elements, and the storage of the resulting image matrix. The raster graphics file is then transmitted from the computer system to the printer via the network. To carry out the method, an electronic printing system is configured, wherein the printing system includes the ability to transmit images to and receive images from a computer system via a network, and the computer system carries out the steps of first and second color separation, the selection and replacement of the image elements, and the storage of the resulting image matrix. When printing the raster graphics file, the embedded color profile is preferably used.

Claims

1. A security document (100) having a colour imprint (104), wherein a first part of the imprint (110) comprises chromatic pigments (114) and in the first part of the imprint (110) the visual impression of an achromatic colour is approximated by the chromatic pigments (114), and wherein a second part of the imprint (112) additionally to chromatic pigments (114) also comprises achromatic pigments (116) of the achromatic colour.

2. The security document (100) according to claim 1, wherein an optical security feature is provided by the imprint (104).

3. The security document (100) according to claim 1 or 2, wherein personalisation information is provided by the imprint (104).

4. The security document (100) according to claim 1, 2 or 3, wherein the achromatic colour has a sensorially detectable property.

5. The security document (100) according to claim 4, wherein the sensorially detectable property is an optical, magnetic, dielectric and / or resistive property.

6. The security document (100) according to any one of the preceding claims, wherein the achromatic colour is IR-visible black or UV-visible black.

7. The security document (100) according to any one of the preceding claims, wherein machine-readable information is provided by dividing the imprint (104) into the first part (110) and the second part (112).

8. The security document (100) according to claim 7, wherein a barcode, a QR code or a digital watermark comprising the machine-readable information is provided by the division of the imprint (104) into the first part (110) and the second part (112).

9. The security document (100) according to claim 7 or 8, wherein the division is pixel-based.

10. The security document (100) according to claim 7, 8 or 9, wherein the division is uncorrelated with a visually perceptible geometric structure of the imprint (104).

11. The security document (100) according to any one of preceding claims 7-10, wherein the machine-readable information is a code for use in a cryptographic method, a cryptographic key or part of a cryptographic key, an identifier, an attribute, a seed value for a cryptographic method and / or a cryptographic certificate or part of a cryptographic certificate.

12. The security document (100) according to any one of preceding claims 7-11, wherein the security document (100) includes an integrated electronic circuit (106) and a memory (126) for storing protection-worthy data (127) and means for executing a cryptographic protocol (122), and has an interface (130) to a reader (132), wherein access of the reader (132) to the protection-worthy data (127) via the interface (130) presupposes the execution of the cryptographic protocol (122) with the aid of the machine-readable information.

13. The security document (100) according to any one of the preceding claims, wherein the security document (100) is a value document, in particular a paper-based and / or plastics-based document, for example an identity document, in particular a machine-readable travel document (MRTD), in particular a passport, personal identity card, visa, driver's licence, vehicle certificate, vehicle registration document, company identification document, health insurance card or another ID document, a chip card, payment means, in particular a bank card, credit card or an electronic payment means, a consignment note or another proof of authority.

14. A method for producing a security document (100) having a colour imprint (104), wherein a first part of the imprint (110) comprises chromatic pigments (114) and in the first part of the imprint (110) the visual impression of an achromatic colour is approximated by the chromatic pigments (114), and wherein a second part of the imprint (112) additionally to chromatic pigments (114) also comprises achromatic pigments (116) of the achromatic colour, said method having the following steps: - providing a document blank (101) and an image, - performing a first colour separation of the image into a number of colour channels so that a first image matrix results, - performing a second colour separation of the image into the number of colour channels and an additional achromatic channel so that a second image matrix results, - selecting pixels of the second image matrix, - replacing pixels of the first image matrix, which correspond in respect of their spatial arrangement in the first image matrix to the selected pixels of the second image matrix, by the respective selected pixels of the second image matrix, - storing the resultant image matrix in the form of a raster graphics file, - printing out the raster graphics file on the document blank by a printer.

15. The method according to claim 14, wherein the printer is a laser printer or dye-sublimation printer or inkjet printer that has three differently coloured inks with chromatic pigments and one ink with achromatic pigments.

16. The method according to claim 14 or 15, wherein the pixels of the second image matrix are selected in dependence on information that is modulated on the printout by replacement of the pixels of the first image matrix.

17. The method according to claim 16, wherein the image is transmitted via a network to a computer system, and the computer system receives or generates the information, and wherein the computer system performs the steps of the first and second colour separation, the selection and replacement of the image elements and also the storing of the resultant image matrix, and the raster graphics file is then transmitted from the computer system via the network to the printer.

18. An electronic printing system which is configured to carry out a method according to any one of preceding claims 15, 16 or 17, wherein the printing system comprises the capability of transmitting images to a computer system and receiving images from said computer system via a network, and the computer system performs the steps of the first and second colour separation, the selection and replacement of the image elements and also the storing of the resultant image matrix.

19. A reader (132) comprising a sensor (146) for detecting an imprint (104) from a security document (100), comprising a colour imprint (104), wherein a first part of the imprint (110) comprised chromatic pigments (114) and in the first part of the imprint (110) the visual impression of an achromatic colour is approximated by the chromatic pigments (114), and wherein a second part of the imprint (112) additionally to chromatic pigments (114) also comprises achromatic pigments (116) of the achromatic colour, and comprising a processor (134) for executing program instructions, wherein the positions of achromatic pigments (116) in an imprint (104) detected by the sensor (146) are detectable by execution of the program instructions, wherein information (118) is derived from the detected positions by execution of the program instructions, comprising means for executing a cryptographic protocol (138) and an interface (140) for communication with the security document (100), wherein access to protection-worthy data (127) of the security document (100) presupposes that the cryptographic protocol (138) has been successfully performed with the aid of the derived information (118).