Method for manufacturing an identity document

Abstract

A method for manufacturing an identity document (10) includes acquiring a set of primary data applicable by light radiation to a first surface area (Z1) of the identity document (10) so as to be visible in ambient light; determining a secondary pattern applicable by light radiation to a second surface area (Z2) so as to be barely visible in ambient light, but visible when backlit by more intense light; calculating a fused digital image comprising the secondary pattern and a subset of primary data intended to be applied to a portion of the first surface area (Z1) overlapping the second surface area (Z2); adding information to be concealed in the fused digital image; and applying by light radiation to the first and second surface areas (Z1,Z2) the set of primary data, the secondary pattern and the concealed information.Figure for the abbreviation: figure 1.

Description

Title of the invention: Method for manufacturing an identity document TECHNICAL FIELD OF THE INVENTION

[0001] The present invention relates to a method for manufacturing an identity document, in particular an identity document comprising a secondary portrait.

[0002] It also relates to an identity document obtained by such a manufacturing process. STATE OF THE ART

[0003] An identity document with a secondary portrait is known from the prior art. It generally comprises a primary image representing the face of the document holder, such as a primary portrait, and a secondary portrait generally representing the same image in smaller dimensions. The primary image and the secondary portrait are integrated into different areas and layers of the document and produced using different technologies to make the document difficult to counterfeit.

[0004] Document FR 3 135 917 is known to be an identity document comprising first and second transparent outer layers and a white central layer, the white central layer comprising a transparent substrate at least partially covered with a white opaque photosensitive coating.

[0005] A secondary portrait can thus be produced by light radiation on the opaque white photosensitive coating, for example by laser ablation or perforation of different points of the opaque white photosensitive coating, so as to be barely visible, i.e. visible with low contrast under ambient light conditions for a human eye, but visible with high contrast when backlit by a light more intense than the ambient light.

[0006] Concealed information is integrated into the secondary portrait, for example using known steganography techniques, in order to enhance security against falsification of the identity document and to guarantee its authenticity.

[0007] A set of primary data is also applied by light radiation to one side of the identity document so as to be visible, i.e., visible with high contrast under ambient light conditions to the human eye. A known technique consists of using a suitable laser to blacken irradiated dots in one of the outer transparent layers of the identity document and thus obtain marking of the primary data.

[0008] This primary data generally consists of personalized data specific to the holder of the identity document, such as alphanumeric characters linked to the holder's identity, called biographical data. It varies in size and length from one holder to another and may occupy a greater or lesser area of ​​the front of the identity document.

[0009] Since the identity document necessarily has a predetermined size, the primary data applied to one side of the identity document are likely to extend into a first surface area which overlaps with a second surface area dedicated to the creation of the secondary portrait to which the concealed information is attached.

[0010] The presence of primary data superimposed on the secondary portrait has the disadvantage of masking, by re-perforating them, areas which contain concealed information and thus preventing proper verification during a check of the authenticity of the identity document.

[0011] One solution is to limit the insertion of hidden information in the secondary portrait to a portion of the secondary portrait that is outside any potential overlap area, regardless of the size and length of the primary data.

[0012] This solution has the disadvantage of drastically reducing the portion of secondary portrait available for steganography and thus reducing the amount of information that can be included in steganography. Description of the invention

[0013] The present invention aims to remedy all or part of the disadvantages of the prior art mentioned above.

[0014] To this end, the invention relates to a method of manufacturing an identity document comprising first and second transparent outer layers and a white central layer, the white central layer comprising a transparent substrate at least partially covered with a white opaque coating sensitive to light radiation.

[0015] The manufacturing process comprises the following steps:

[0016] - Acquisition of a set of primary data intended to be applied by light radiation onto a first surface area of ​​the identity document so as to be visible under ambient light conditions to the human eye; and

[0017] -Determination of a secondary pattern intended to be applied by light radiation to a second surface area of ​​the identity document so as to be barely visible under ambient light conditions to the human eye, but visible when backlit by a light more intense than the ambient light.

[0018] According to the invention, the method for manufacturing an identity document further comprises the following steps:

[0019] - Calculation of a fused digital image including said secondary motif and at less a subset of said primary data set, said subset comprising primary data intended to be applied to a portion of the first surface area covering said second surface area;

[0020] - Obtaining information to be concealed in said merged digital image;

[0021] - Addition of said information to be concealed in said merged digital image; and

[0022] - Application by light radiation on the first surface area and the second surface area of ​​the identity document of said primary data set, secondary pattern and said concealed information.

[0023] Thus, the information to be concealed is determined by taking into account the secondary motive and the part of the primary data which is intended to cover the secondary motive on the final identity document.

[0024] The concealed information of the type steganography or watermarking (Anglo-Saxon term for information in watermark or visible or invisible tattoo) can thus grant protection not only to the secondary motif but also to the subset of said primary data set of the merged digital image, thereby improving the robustness against falsification and counterfeiting of the identity document.

[0025] Since the information to be concealed is also added to the merged digital image, it is not likely to be obscured by a portion of the primary data which would be subsequently applied to a portion of the first surface area covering the second surface area, which would hinder the subsequent decoding of this concealed information to verify the authenticity of the identity document.

[0026] Advantageously, at the calculation stage, said subset includes all the primary data intended to be applied to the portion of the first surface area covering said second surface area.

[0027] The secondary pattern is therefore not limited in size in the second surface area of ​​the identity document, the information to be concealed can be added throughout the second surface area of ​​the identity document without risk of being masked by part of the primary data.

[0028] Advantageously, at the application stage, the light radiation performs an ablation of the opaque white photosensitive coating in said second surface area of ​​the identity document.

[0029] It is possible to obtain a secondary pattern in the second surface area of ​​the document without weakening the structure of the body of the identity document.

[0030] Preferably, the light radiation performs an ablation of several points of the opaque white photosensitive coating so that the points exposed to the light radiation become transparent and form a pattern corresponding to said fused digital image incorporating said hidden information.

[0031] The entire fused digital image is produced by ablation of points of the opaque white photosensitive coating, so that the concealed information can be made visible, highly contrasted and authenticated when the second surface area of ​​the identity document is backlit by a light more intense than the ambient light.

[0032] In practice, the diameter of each point is less than 50 pm.

[0033] Each point, taken individually, is barely visible under ambient light conditions to a human eye, but visible when backlit by a light more intense than the ambient light.

[0034] By increasing the number of points produced by ablation of the opaque white photosensitive coating, it is possible to obtain a part of the pattern visible under ambient light conditions to a human eye.

[0035] Advantageously, at the application stage, the light radiation causes a blackening of several points of one of said first and second external transparent layers so as to form a visible pattern corresponding to primary data of said set in said first surface area but outside said portion of the first surface area covering said second surface area of ​​the identity document.

[0036] In an advantageous embodiment of the method for manufacturing an identity document, at the application stage, a single laser is implemented, the power of the laser being set in a first range of values ​​for the application by light radiation of primary data of said assembly in said first surface area but outside said portion of the first surface area covering said second surface area of ​​the identity document, and in a second range of values, lower than the values ​​of said first range, for the application of primary data, of the secondary pattern and of said information concealed in said second surface area.

[0037] Thus, all the primary data, the secondary pattern and the concealed information can be applied by the same laser operating at different powers, facilitating the positioning of all the marks to be printed on the identity document and avoiding the steps of relative positioning of the different marks to each other in the surface of the identity document.

[0038] During the laser application of the primary data, secondary pattern, and concealed information, only an overall positioning of the data to be applied to the first and second surface areas of the identity document needs to be determined. Adjusting the laser power allows the primary data to be applied, on the one hand, to the visible primary data in the first surface area but outside the second surface area, and on the other hand, to the less visible data in the second surface area.

[0039] In practice, the only laser used is an Nd:YAG solid state laser or a Yb-doped fiber laser, emitting infrared laser radiation, at a wavelength between 700 and 2500 nm, and for example equal to 1064 nm.

[0040] According to a second aspect, the invention relates to an identity document manufactured according to the manufacturing process described above, comprising first and second transparent outer layers and a white central layer, the white central layer comprising a transparent substrate at least partially covered with a photosensitive white opaque coating, primary data being visible on a first surface area of ​​the identity document under ambient light conditions for a human eye, and a secondary pattern and concealed information being barely visible on a second surface area of ​​the identity document under ambient light conditions for a human eye, but visible when backlit by a light more intense than the ambient light.

[0041] This identity document has the advantage of being able to include a secondary motif incorporating concealed information of the steganographic type over a large area of ​​the document despite the presence of primary data resulting in perforated areas corresponding, for example, to the thickness of the fonts, while respecting the micro unperforated areas necessary for the concealment of information, and this, without harming either the readability of the characters or that of the concealed information. BRIEF DESCRIPTION OF THE FIGURES

[0042] Other features and advantages of the invention will become apparent from the following non-limiting description.

[0043] To the attached drawings, given by way of non-limiting example:

[0044] - Fig. 1 is a top view of an identity document according to a mode of realization of the present invention;

[0045] - Figure [Fig. 2] is a schematic cross-sectional view of an identity document according to one embodiment of the invention;

[0046] - Figure 3 is a flowchart describing one embodiment of the process of manufacturing of the present invention;

[0047] - Figures 4A, 4B, 4C and 4D illustrate the different stages of the process of manufacturing of [Fig. 3]; and

[0048] - Figure 5 presents a schematic curve illustrating the adjustment of a laser set in work in an embodiment of the manufacturing process according to the invention. DETAILED DESCRIPTION OF THE INVENTION

[0049] We will first describe, with reference to [Fig. 1], an example of an identity document according to one embodiment of the invention.

[0050] Of course, the examples of embodiment given above are by no means limiting, particularly with regard to examples of dimensions or materials.

[0051] The identity document 10 may be an identity card, a driver's license, a bank card, a credit card, an identity card, or an official document in the form of a booklet, such as a passport. These identity documents are used to verify the identity of their holder.

[0052] Generally, such an identity document comprises a flat body delimiting an upper face and a lower face, the body being formed by one or more layers of PC, or PVC or PET or any combination of these materials.

[0053] Typically, one side 10a of the identity document includes a first portrait 11, such as an official photograph of the document holder, this first portrait 11 conforming to certain specific government regulations. The first portrait 11 may be produced by printing on one of the sides of the identity document 10, and here on the upper side 10a of the identity document 10.

[0054] The remaining portion of the upper face 10a of the identity document 10 includes several security features such as a secondary portrait of the holder. This secondary portrait allows the authenticity of the identity document to be verified.

[0055] As schematically visible in [Fig.2], the identity document 10 is formed of a body 12 made up of several stacked substrates, and at least three substrates: a first transparent outer layer 121, forming for example the upper face 10a of the identity document 10, a second transparent outer layer 122 forming the lower face 10b of the identity document 10 and a central white layer 123 with a transparent substrate 123b at least partially covered with a white opaque photosensitive coating 123c, between the two transparent outer layers 121,122.

[0056] Each substrate can be made of a polymer material such as PVC, Polycarbonate, PET or any combination of these materials.

[0057] The white central layer 123 may have a white opaque photosensitive coating over its entire surface or only over a portion forming a window and covered with the white opaque photosensitive coating

[0058] In the embodiment illustrated in [Fig.2], the central white layer 123 comprises a white opaque layer 123a with a window in which is inserted a transparent substrate 123b covered with a white photosensitive opaque coating 123c.

[0059] The opaque white photosensitive coating 123c is made of a thin metallic film with an optical grating on its surface to obtain a white appearance, or of a white-appearing metal oxide, applied to a transparent polymer substrate 123b. This thin film is a few nanometers thick so as to be easily laser-perforated.

[0060] The photosensitive thin film can be produced by a process known in the prior art, for example, plasma processes such as PVD (physical vapor deposition) in a plasma reactor. This deposition is carried out on a substrate intended to be subsequently deposited hot onto a layer of polycarbonate. Alternatively, the photosensitive thin film can be deposited directly onto the polycarbonate.

[0061] The thin film is sensitive to light 21, such that the thin film is perforated when exposed to this light 21. The light 21 can be applied by a laser. When the light 21 is applied to the thin film, the area of ​​the thin film exposed to the radiation is locally perforated, revealing the transparent polycarbonate layer at the perforation point. Alternatively, a photosensitive material can be used, the physical and / or chemical transformation of which results in a change from opacity to transparency. This transformation of the thin film's structure results in a localized decolorization or bleaching of the film's pigments. The area modified by the radiation is limited / localized to the point of contact of the radiation on the thin film.

[0062] The light radiation 21 can thus perform an ablation of several points of the opaque white photosensitive coating so that the points exposed to the light radiation become transparent and form a pattern made up of micro holes barely visible under ambient lighting and visible in backlighting.

[0063] Throughout the description, a point or pattern is characterized as "visible" under ambient lighting conditions or ambient light, or backlit by light more intense than ambient light, when it is visible to a human eye, to the naked eye, that is, visible with a strong contrast with its surroundings, such as a juxtaposed color.

[0064] Conversely, a point or pattern is said to be "low visibility" when it exhibits low contrast with its surroundings under ambient lighting conditions, and is difficult or impossible to see with the naked eye. Contrast refers to a characteristic of the human eye's perception of the difference in color or brightness between a point or pattern and its surroundings.

[0065] The diameter of each spot made by ablation is less than 50 pm, so that each spot is barely visible under ambient light conditions to a human eye, but visible when backlit by a light more intense than the ambient light.

[0066] The first and second outer layers 121, 122 are sensitive to light radiation 21, but only react by carbonization when exposed to the same light radiation at a higher energy. The sensitivity threshold depends not only on the wavelength and output energy of the laser used to apply the light radiation, but also on additives such as carbon, but not exclusively, which make the material of the first and second outer layers 121, 122 sensitive to the laser.

[0067] Only the thin layer of metal oxide 123c is locally transformed by low-energy light radiation 21.

[0068] Returning to [Fig. 1], the identity document 10 is designed to be personalized and to receive information specific to the identity of the holder of the identity document 10 according to different techniques of applying this information to the identity document.

[0069] A set of primary data is first intended to be applied by light radiation to a first surface area of ​​the identity document so as to be visible under ambient light conditions to a human eye.

[0070] Primary data include, for example, biographical data such as name, country, date of birth, date of issue and expiry of identity document...

[0071] As seen in [Fig.1], this primary data set is visible on a first area ZI of the surface of the identity document, and here, on the upper face 10a of the identity document 10.

[0072] A secondary pattern is further intended to be applied by light radiation to a second surface area Z2 of the identity document 10 so as to be barely visible under ambient light conditions to a human eye, but visible, because of high contrast, when backlit by a light more intense than the ambient light.

[0073] This secondary motif is, for example, a secondary portrait, determined from the first portrait 11 intended to be printed on the identity document. This secondary motif may include various authentication elements specific to the identity document 10, for example, information concealed within the secondary portrait. Known information insertion techniques, such as steganography or watermarking, may be implemented.

[0074] As illustrated in [Fig.1], the first surface area Z1 and the second surface area Z2 overlap, as do the information applied respectively to these two surface areas Z1, Z2.

[0075] In this embodiment, the first surface zone Zl that overlaps the second surface zone Z2 corresponds to the second surface zone Z2. Of course, the overlap of the second surface zone Z2 by the first surface zone Zl could only be partial.

[0076] We will now describe, in relation to [Fig.3] and illustrative figures 4A to 4D, a manufacturing process for such an identity document 10.

[0077] The manufacturing process is applied to an identity document 10 formed of a body 12 as described above in view of [Fig.2].

[0078] The different layers of the body 12 of the identity document 10, i.e. the first and second transparent outer layers 121, 122 and the central white layer 123 are assembled for example by hot lamination to form the body 12 of the identity document 10.

[0079] The manufacturing process includes an acquisition step E31 of the primary data set intended to be applied by light radiation to a first surface area Zl of the identity document 10 so as to be visible under ambient light conditions to a human eye.

[0080] An example of such a primary data set is illustrated in [Fig.4A].

[0081] The manufacturing process also includes a step E32 of determining the secondary pattern intended to be applied by light radiation to a second surface area Z2 of the identity document 10 so as to be barely visible.

[0082] An example of such a secondary motif is illustrated in [Fig.4B].

[0083] The manufacturing process includes a calculation step E33 of a fused digital image comprising the secondary pattern and at least a subset of the primary data set.

[0084] This subset of primary data includes primary data intended to be applied to a portion of the first surface area Z1 covering the second surface area Z2.

[0085] An example of such a merged digital image is illustrated in [Fig.4C].

[0086] In this embodiment, the primary data subset comprises all the primary data intended to be applied to the portion of the first surface area Z1 covering the second surface area Z2.

[0087] Thus, as illustrated in [Fig.4D], the complement of this subset of primary data corresponds to the primary data intended to be applied outside the second surface area Z2 of the identity document 10.

[0088] The manufacturing process further includes a step E34 of obtaining information to be concealed in the fused digital image.

[0089] The information to be concealed may consist of one or more pixels to be added to a pixel of the merged digital image, or of the modification of a pixel of this merged digital image itself.

[0090] Thanks to the calculation step E33, the information to be concealed can be integrated into a large-dimensional fused digital image, which can occupy the entire surface of the second surface area Z2 dedicated to the application of a secondary pattern.

[0091] Furthermore, the merged digital image taking into account the subset of primary data intended to be applied over the second surface area Z2, the information to be concealed can also be inserted into a part of this subset of primary data and remain accessible and decodable to authenticate the identity document.

[0092] The manufacturing process then includes a step E35 of adding the information to be concealed in the merged digital image.

[0093] This addition of information to be concealed in a digital image is known in the techniques of steganography or watermarking and does not need to be detailed here.

[0094] The manufacturing process finally includes an application step E36 by light radiation on the first surface area ZI and the second surface area Z2 of the identity document 10 of the primary data set, the secondary pattern and the concealed information.

[0095] The same light radiation 21, 22 from a laser causes an ablation of the opaque white photosensitive coating 123c of the central white layer 123 under low energy and a blackening of points of one of the external transparent layers 121, 122 under high energy.

[0096] In practice, the low-energy light 21 ablates several points of the opaque white photosensitive coating so that the perforated points form a pattern that is barely visible except for large areas consisting of wide perforation zones, for example, characters. This area perforated by low-energy light 21 corresponds to the fused digital image incorporating the hidden information, i.e., the digital image as obtained after the addition step E35.

[0097] This pattern is produced in the second surface area Z2 of the identity document 10, at the level of the central white layer 123.

[0098] This pattern, barely visible except for the widely perforated areas such as the characters, thus corresponds to the information illustrated in [Fig.4C].

[0099] By using sufficiently thick fonts, the texts produced by perforation in the second surface area Z2 are visible thanks to the surface The important thing is that these characters form a significant image. On the other hand, the image corresponding to the secondary portrait remains barely visible except under backlighting.

[0100] In this embodiment, a high-energy beam of light 22 blackens several points of the first outer transparent layer 121, on the upper surface 10a of the identity document 10, so as to form a pattern visible in areas where the photosensitive film is not present and where it is replaced by a white polymer core such as PET or PC. The contrast of the marking is achieved by carbonization.

[0101] This visible pattern corresponds here to the primary data applied in the first surface area ZI but outside the portion of the first surface area ZI which covers the second surface area Z2 of the identity document 10.

[0102] This visible pattern thus corresponds to the information illustrated in [Fig.4D].

[0103] In practice, during the application step, a single laser is used.

[0104] The laser used is for example an Nd:YAG solid state laser or a Yb-doped fiber laser, emitting infrared laser radiation, at a wavelength between 700 and 2500 nm, and for example equal to 1064 nm.

[0105] The wavelength of the radiation will be chosen according to the properties of the metal oxide thin film. In particular, the metal oxide thin film must be sensitive to the chosen laser radiation to allow laser ablation.

[0106] As illustrated in [Fig.5], the laser power is adjustable and can be controlled for example by pulse width modulation (PWM).

[0107] The laser power is controllable over its entire power range.

[0108] As illustrated in [Fig. 5], a greyscale image (in Anglo- terminology Saxon "grayscale") has pixels with values ​​between 0 and 255, with white corresponding to the value 255 and black to the value 0: the higher the pixel value, the lighter or whiter the pixel.

[0109] Any laser energy level can be associated with a particular pixel value. To represent a grayscale image, the laser power is generally linearized to obtain the same rendering as the image. Therefore, the aim is to have maximum energy when the pixel has a value of 0, and no energy when the pixel has a value of 255.

[0110] In practice, the image engraved in the second surface area Z2 has few grey levels (2 minimum) so as to have low contrast in the second surface area Z2. An image is created with as many pixel values ​​as there are grey levels, and for example here 2: for example pixels with values ​​of 255 and 250.

[0111] The laser is then configured to have no perforation of the thin photosensitive film 123c at the pixel value equal to 255 and a perforation of size maximum of the 123c photosensitive thin film for the pixel value equal to 250. In practice, the energy required to puncture the 123c photosensitive thin film is very low.

[0112] The primary data set to be applied in the first surface area Z1, but outside the portion of the first surface area Z1 that overlaps the second surface area Z2 of the identity document 10, is engraved onto the outer polycarbonate layer by applying higher-energy laser radiation 22 to carbonize the polycarbonate. In practice, characters corresponding to the primary data are created with lower-value pixels for which the laser is set to a higher energy.

[0113] If only text is to be engraved as primary data, only a single pixel value corresponding to one gray level for maximum laser energy will be used. If primary data with multiple gray levels is to be engraved on polycarbonate, several laser energy values ​​can be used, in addition to those selected for perforating the 123c photosensitive thin film.

[0114] The primary data which are to be applied in the first surface area Zl, but outside the portion of the first surface area Zl which covers the second surface area Z2 of the identity document 10 are represented by pixels with values ​​less than a threshold value S, and the complementary primary data, intended to be applied on the second surface area Z2 as well as the secondary pattern and the concealed information are represented by pixels with values ​​greater than this threshold value S.

[0115] By way of non-limiting example, this threshold pixel value may be between 220 and 240, and for example be substantially equal to 230.

[0116] Thus, to each pixel coded between 0 and 255 to represent respectively the primary data set, the secondary pattern and the hidden information, a defined energy can be associated for the light radiation used.

[0117] When a single laser is implemented, the laser power is set in a first range of values ​​for the application by light radiation of primary data in the first surface area Zl, but outside the portion of the first surface area Zl covering the second surface area Z2, and in a second range of values, higher than the values ​​of the first range, for the application of primary data, the secondary pattern and the information hidden in the second surface area Z2.

[0118] In practice, the laser power is set to a first energy value for the application by light radiation of primary data by carbonization in the first surface area Zl but outside the portion of the first surface area Zl covering the second surface area Z2 of the identity document 10.

[0119] The first power value of the laser is chosen such that the light radiation 22 causes blackening by carbonization of the first transparent layer 121, at different points to form a visible pattern corresponding to a part of the primary data as seen in [Fig.4D].

[0120] The laser power is set to a second range of values ​​for the application by light radiation of primary data, of the secondary pattern and of the information concealed in the second surface area Z2.

[0121] The second range of values ​​is chosen such that the light radiation 21 applied to the white intermediate layer 123 creates small transparent holes or dots in the thin metal oxide film 123c. The diameter of the holes varies according to the laser energy but never causes carbonization of the outer transparent layers 121 or 122.

[0122] The laser light 21 is applied to several points on the photosensitive layer in order to form the fused image incorporating the hidden information. In particular, it allows the formation of the secondary pattern contours and the reproduction of the subset of primary data on the second surface area Z2 as illustrated in [Fig. 4C].

[0123] Each of the transparent dots has very small dimensions, less than approximately 50 µm, in diameter or in cross-section. Consequently, in ambient light, these transparent dots are barely visible to the human eye at a normal viewing distance of approximately 30 to 40 cm under frontal illumination. However, these transparent dots become visible to the human eye under ambient light conditions when numerous transparent dots are placed side by side to form the thickness of the text characters corresponding to the primary data intended to be applied to the portion of the first surface area Z1 that overlaps the second surface area Z2.

[0124] Thus, the personalization of biographical information (alphanumeric data, text) in the first surface area ZI but outside the second surface area Z2 is done by carbonization of certain transparent layers 212, 122 sensitive to laser.

[0125] The laser energy that reaches the white central layer 123 is strong but does not cause damage to the white polycarbonate.

[0126] However, the personalization of biographical information (alphanumeric data, text) in the second surface area Z2 does not generate any carbonization. The laser energy is much lower but sufficient to penetrate the white photosensitive layer 113c.

[0127] It is important to limit the laser energy reaching the photosensitive white layer 123c in order to avoid degrading the latter (appearance of pockets of gases that would delaminate the structure of the identity document and present bubbles visible to the naked eye).

[0128] When the identity document 10 is under dominant frontal light on the upper surface 10a (front) as opposed to backlighting on the lower surface 10b (back), the human eye sees the perforated areas as dark. This "black on white" contrast of the characters makes the text easy to read.

[0129] The other perforated holes that form the secondary image are smaller than the thickness of the characters forming the biographical data text. The secondary image is therefore not very visible or barely visible under frontal lighting. However, the secondary image becomes visible and highly contrasted when backlit on the lower surface 10b (reverse side) of the identity document. The observer sees the text in negative and superimposed on the secondary image, but this does not prevent correct identification of the photograph corresponding to the secondary image.

[0130] In practice, an overall image including all the information to be printed (primary data set, secondary pattern and hidden information) is recorded and positioned on the surface of the identity document 10 according to the location and dimensions of the first surface area ZI and the second surface area Z2 on the upper face 10a of the identity document 10.

[0131] A compromise is calculated in order to optimally position this information in the first and second surface zones Zl, Z2.

[0132] The manufacturing process thus makes it possible to obtain an identity document 10 with a large secondary motif, and a steganography or watermarking which remains authenticable, despite the presence of primary data which come superimposed with the secondary motif.

[0133] Of course, the present invention is not limited to the embodiments described above.

[0134] In particular, different lasers can be used to carry out on the one hand the application by blackening or carbonization of the primary data on the upper face 10a of the identity document 10, and on the other hand, the ablation of the opaque white photosensitive coating to produce the fused image incorporating the concealed information.

Claims

Demands

1. Method of manufacturing an identity document (10) comprising first and second external transparent layers (121, 122) and a white central layer (123), the white central layer (123) comprising a transparent substrate (123b) at least partially covered with a white opaque photosensitive coating (123c), said manufacturing method comprising the following steps: - Acquisition (E31) of a set of primary data intended to be applied by light radiation to a first surface area (Zl) of the identity document (10) so as to be visible under ambient light conditions to a human eye;-Determination (E32) of a secondary pattern intended to be applied by light radiation to a second surface area (Z2) of the identity document (10) so as to be barely visible under ambient light conditions to the human eye, but visible when backlit by light more intense than ambient light; Characterized in that it further comprises the steps of: - Calculation (E33) of a fused digital image comprising said secondary pattern and at least a subset of said primary data set, said subset comprising primary data intended to be applied to a portion of the first surface area (Z1) covering said second surface area (Z2); - Obtaining (E34) information to be concealed in said fused digital image; - Adding (E35) said information to be concealed in said fused digital image;and - Application (E36) by light radiation on the first surface area (Z1) and the second surface area (Z2) of the identity document (10) of said primary data set, of the secondary pattern and of said concealed information.;

2. Method of manufacturing an identity document according to claim 1, characterized in that at the calculation step (E33), said sub-assembly includes all the primary data intended to be applied to the portion of the first surface area (Z1) covering said second surface area (Z2).

3. Method of manufacturing an identity document according to one of claims 1 or 2, characterized in that at the application step (E36), the light radiation (21) performs an ablation of the opaque white photosensitive coating (123c) in said second surface area (Z2) of the identity document (10).

4. A method for manufacturing an identity document according to claim 3, characterized in that the light radiation (21) performs an ablation of several points of the opaque white photosensitive coating so that the points exposed to the light radiation become transparent and form a pattern corresponding to said fused digital image incorporating said concealed information.

5. Method of manufacturing an identity document according to claim 4, characterized in that the diameter of each point is less than 50 pm.

6. A method for manufacturing an identity document according to any one of claims 1 to 5, characterized in that at the application step (E36), the light radiation (22) causes a blackening of several points of one of said first and second external transparent layers (121, 122) so as to form a visible pattern corresponding to primary data of said assembly in said first surface area (Z1) but outside said portion of the first surface area (Z1) covering said second surface area (Z2) of the identity document (10).

7. A method for manufacturing an identity document according to any one of claims 1 to 6, characterized in that at the application step (E36), a single laser is implemented, the power of the laser being set in a first range of values ​​for the application by light radiation of primary data of said assembly in said first surface area (Z1) but outside said portion of the first surface area (Z1) covering said second surface area (Z2) of the identity document (10), and in a second range of values, lower than the values ​​of said first range, for the application of primary data, of the secondary pattern and of said information concealed in said second surface area (Z2).

8. A method for manufacturing an identity document according to claim 7, characterized in that the single laser used is

9. a solid-state Nd:YAG laser or a Yb-doped fiber laser, emitting infrared laser radiation, at a wavelength between 700 and 2500 nm, and for example equal to 1064 nm. Identity document manufactured according to the manufacturing process according to any one of claims 1 to 8, characterized in that it comprises first and second external transparent layers (121, 122) and a white central layer (123), the white central layer (123) comprising a transparent substrate (123b) at least partially covered with a white opaque photosensitive coating (123c), primary data being visible on a first surface area (Z1) of the identity document (10) under ambient light conditions for a human eye, and a secondary pattern and concealed information being barely visible on a second surface area (Z2) of the identity document under ambient light conditions for a human eye, but visible when backlit by light more intense than ambient light.

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