Personalized security document and method of manufacturing the same

Abstract

A personalized security document (10) includes a first personalized image (5) and a second personalized image (8) as part of a security feature (3). The second personalized image (8) is arranged at a position that corresponds to the first personalized image (5). For example, the first personalized image (5) is laser-engraved in a first surface (6a) of a laser-engravable material layer (6). The second personalized image (8) may be formed by laser-engraving on a second surface (6b) opposite to the first surface (6a) of the laser-engravable material layer (6). Alternatively or additionally, the second personalized image (8) may be formed by printing onto a substrate (1) of the security document (10) of the laser-engravable material layer (6) to form a personalized variable watermark.

Description

DescriptionPERSONALIZED SECURITY DOCUMENT AND METHOD OF MANUFACTURING THE SAMETechnical Field

[0001] The present disclosure generally relates to security features for security documents, in particular, personalizable security documents such as identification documents, driver’s licenses and the like.Background

[0002] Generally, in the market of physical identification documents, a variety of different security features are used to ensure the document’s security and integrity. In some applications, a laser-engraved image is considered vital, as the image features are generated inside a polycarbonate substrate rather than on the surface of the substrate making it more difficult to tamper with the document. A laser-engraved feature in a polycarbonate substrate may include a black and white (in particular, grayscale) image, a color image, or special features like the Mirage security feature of HID.

[0003] WO 2022 / 248309 Al discloses a personalizable security document including a combination of a plurality of different features. In particular, a laser-engraved image is provided in a first layer of the security document, and one or more fluorescent inks are provided in further layers of the same. A laser-engraving of the image is performed from a first side of the substrate, such that patterns formed by the fluorescent inks are not affected. Under white light, the laser-engraved image can be viewed from the first side, whereas a multi-color fluorescence of the patterns can be observed from a second side under UV light.

[0004] The present disclosure is directed, at least in part, to improving or overcoming one or more aspects of prior systems, without being limited to a particular type of security document.Summary of the Disclosure

[0005] According to one aspect of the present disclosure, a personalized security document includes a substrate having a first side and a second side opposite to the first side in a thickness direction of the substrate, and a security feature formed in the substrate and extending through at least part of the substrate along the thickness direction. The security feature has a laser-engravable material layer including a first personalized image laser engraved in a first surface of the same. The laser-engravable material layer exhibits a color-change effect upon irradiation with laser light. The first personalized image is visible when the substrate is viewed from the first side under white light. The security feature further includes a second personalized image formed at a position that corresponds to the laser-engravable material layer, the second personalized image being visible when the substrate is viewed from one of the first side and the second side under white light.

[0006] In another aspect of the present disclosure, a method of manufacturing a personalized security document includes the steps of providing a substrate having a first side and a second side opposite to the first side in a thickness direction of the substrate, the substrate including a laser-engravable material layer exhibiting a color-change effect upon irradiation with laser light, and forming a security feature in the substrate, the security feature extending through at least part of the substrate along the thickness direction. The security feature is formed by laser engraving a first personalized image in a first surface of the laser-engravable material layer by irradiating laser light onto the same from the first side, the first personalized image being visible when the substrate is viewed from the first side under white light, and forming a second personalized image at a position that corresponds to the laser-engravable material layer, the second personalized image being visible when the substrate is viewed from one of the first side and the second side under white light.

[0007] Other features and aspects of the present disclosure will be apparent from the following description and the accompanying drawings.Brief Description of the Drawings

[0008] Fig. 1 shows a plan view of an exemplary personalized security document in accordance with the present disclosure;Fig. 2 shows a security feature provided in a security document in accordance with a first embodiment of the present disclosure;Fig. 3 shows several exemplary configurations of a laser- engravable material layer including a first personalized image and a second personalized image;Fig. 4 shows another exemplary configuration of a laser- engravable material layer including a first personalized image and a second personalized image;Fig. 5 shows a security feature provided in a security document in accordance with a second embodiment of the present disclosure;Fig. 6 shows different views of the security feature of the second embodiment;Fig. 7 shows several examples of further combinations of a first personalized image and a second personalized image in accordance with the present disclosure;Fig. 8 shows another example of a security feature in accordance with the present disclosure; andFig. 9 illustrates an exemplary method of manufacturing a personalized security document in accordance with the present disclosure.Detailed Description

[0009] The following is a detailed description of exemplary embodiments of the present disclosure. The exemplary embodiments described herein are intended to teach the principles of the present disclosure, enabling those of ordinary skill in the art to implement and use the present disclosure in many different environments and for many different applications. Therefore, the exemplary embodiments are not intended to be, and should not be considered as,a limiting description of the scope of protection. Rather, the scope of protection shall be defined by the appended claims.

[0010] The present disclosure is based at least in part on the realization that, although personalization features are the most valuable features on security documents such as passports and ID cards, there is currently a limited set of features which can be personalized. For example, in the Mirage feature of HID, a security document is only personalized on a first side of the same, using a single technology.

[0011] It has been realized that the security of the document can be further enhanced by performing at least one further personalization of the security feature of the document, either from the opposite side or from the same side. Here, a variety of different techniques can be combined, for example, a first personalized image can be created by laser-engraving, similar to the Mirage feature of HID, and a second personalized image can be formed by printing, for example, using known ink-jet printing techniques.

[0012] It has also been realized that some kinds of laser-engravable materials, such as the material that is used for the Mirage feature of HID, are inherently capable of being laser-engraved from both sides of the corresponding material layer, provided that any additional layers above or below the laser- engravable material layer, if present, are transparent for the laser light used. This can be used in an advantageous manner to provide the first personalized image by laser engraving a first surface of the laser-engravable material, and the second personalized image by laser engraving an opposite second surface of the laser- engravable material. Here, it will be appreciated that the laser-engraving from both sides is difficult to reproduce without having detailed knowledge of the laser powers and other parameters to be used for the engraving, in particular, depending on the thickness of the material layer. In this manner, the security can be further enhanced, because it becomes even more difficult to forge a security document including such a feature.

[0013] Finally, it has also been realized that the above-mentioned first and second personalized images can also be combined with a further security feature such as a watermark in order to obtain an even more complex security feature that is even more difficult to reproduce.

[0014] Fig. 1 shows a plan view of an exemplary personalized security document 10 in accordance with the present disclosure. As shown in Fig. 1, security document 10 includes a substrate 1, for example, having a substantially rectangular shape. In particular, as shown in Fig. 1, security document 10 is a personalized security document, i.e., includes an image 11, for example, a photograph or the like, of a person to which the document belongs. Image 11 can be formed in image region 2 provided on a first side SI of substrate 1 in a known manner.

[0015] In addition, as shown in Fig.l, document 10 includes a security feature 3 formed in substrate 1, which is a window having, for example, a rectangular shape and in which one or more secure features may be provided. For example, as shown in Fig. 1, security feature 3 may include a laser-engraved first personalized image 5, which may correspond to image 11 (for example, be an inverse or negative of image 11), in a laser-engravable material layer 6 of security feature 3. This will be described in more detail in the following.

[0016] It will be appreciated that, after manufacturing, security document 10 may be a personalizable security document. In other words, image region 2 and laser-engravable material layer 6 may not be processed, such that security document 10 is not personalized. Generally, such personalization will be carried out by the respective issuers of the security documents, for example, passports, identification cards, driver’s licenses or the like. The result of this personalization is a personalized security document such as personalized security document 10 described herein.

[0017] Fig. 2 shows a schematic sectional view of personalized security document 10. As shown in Fig. 2, personalized security document 10 has substrate 1 having first side SI and a second side S2 opposite to first side SI in athickness direction d of substrate 1. For example, substrate 1 may be formed by stacking a plurality of layers, for example, polycarbonate, TPU and / or PVC layers, and combining them in an appropriate manner, for example, by a lamination process or the like. This is known to the skilled person, such that a detailed description will be omitted herein.

[0018] In a first embodiment, a security feature 3a is formed in substrate 1 and extends through at least part of substrate 1 along thickness direction d. In the example shown in Fig. 2, security feature 3a extends from the uppermost layer to the bottom layer of substrate 1. In some embodiments, at least the portion of each layer in which security feature 3a is formed is substantially transparent or at least semi-transparent for visible light, such that laser-engravable material layer 6 is visible from both sides of security document 10.

[0019] As shown in Fig. 2, security feature 3a includes laser-engravable material layer 6 including first personalized image 5 laser engraved in a first surface 6a of the same. For example, laser-engravable material layer 6 may be formed as a material layer on one of the layers forming substrate 1 of security document 10. For example, an ink may be applied onto a surface of one of the layers of substrate 1, for example, prior to laminating the different layers of substrate 1 to form security document 10. In other embodiments, laser-engravable material layer 6 may be formed in a different manner, either on a layer of substrate 1, or in a layer of the same. In any case, laser-engravable material layer 6 has a predetermined thickness in thickness direction d, for example, between 1 pm and 100 pm, preferably between 10 pm and 50 pm.

[0020] The material of laser-engravable material layer 6 has a property such that laser-engravable material layer 6 exhibits a color-change effect upon irradiation with laser light. As used herein, the “color-change effect upon irradiation with laser light” means that laser light that is irradiated onto laser- engravable material layer 6 changes at least one physical property of, for example, particles or pigments included in laser-engravable material layer 6 in a predetermined manner, for example, depending on the intensity of the laser light,and / or other laser parameters. One particular example is the ink that is used in the Mirage feature of HID. In this technology, each pixel in the laser-engraved first personalized image 5 has a defined color value, depending, for example, on a digital grayscale value of a grayscale image to be engraved. For example, a color value of blue corresponds to white in the digital grayscale image to be engraved, and a color value of gold corresponds to black in the digital grayscale image to be engraved. This means that, for example, a minimum or zero laser power results in that laser-engravable material layer 6 remains of an initial blue color, whereas increasing laser power results in a color change from the initial blue color towards a golden color at maximum laser power. In between the minimum and the maximum laser power, a color-change can be observed from blue to gold. In this manner, for example, a grayscale portrait of a holder of security document 10, for example, a negative or positive image of image 11, can be formed in first surface 6a of laser-engravable material layer 6.

[0021] Here, it will be appreciated that the present application is not limited to the Mirage ink described above, and can be applied to any known laser-engravable material that exhibits a color-change effect when irradiated with laser light. However, it is important to note that the color-change effect as described herein is different from a change that is obtained when a physical structure of a material layer such as a transparent PVC layer or the like is modified by being burnt using a laser having a certain power. It will be appreciated that in such a manner a grayscale image can be formed in a top layer of substrate 1, however, such a formation of a grayscale image by burning of the material of the layer is not to be understood as exhibiting a color-change effect in accordance with the present disclosure. Accordingly, as used herein, a material that exhibits a color-change effect is to be considered a material which changes its color from a first, in particular, chromatic color (for example, blue) to a second, different color (for example, golden), and a change from, for example, colorless to gray or black due to burning of material with increasing laser power is not to be considered as a color-change effect.

[0022] Returning to Fig. 2, laser-engravable material layer 6 may be formed on a first layer 16 of substrate 1. For example, the above-mentioned laser- engravable ink may be formed on a bottom surface of first layer 16, for example, by screen printing or the like. It will be appreciated, however, that in other embodiments laser-engravable material layer 6 may be formed on a top surface of first layer 16 or another layer of substrate 1. Additionally, first layer 16 may be covered by one or more additional layers, such as protective layers (not shown). In other applications, first layer 16 may be the top layer of the stack of layers of substrate 1. In any case, the stack of layers of substrate 1 is configured such that first personalized image 5 can be laser-engraved in laser-engravable material layer 6 from first side SI using an appropriately configured laser, in particular, having a predetermined wavelength. In the example of the HID’s Mirage feature, this wavelength may be, for example, 1000-1100 nm. It will be appreciated that, in particular, when first layer 16 is covered by one or more additional layers, said additional layers are transparent for the laser light, and the laser parameters are controlled such that the material of the additional layers is not visibly modified (i.e. burned) by the laser.

[0023] As initially mentioned, in accordance with the present disclosure, security feature 3a includes a second personalized image 8 (see, for example, Fig. 3) formed at a position that corresponds to laser-engravable material layer 6. Second personalized image 8 is visible when substrate 1 is viewed from one of first side SI and second side S2 under white light (i.e., in reflection under normal lighting conditions). The same applies to first personalized image 5 when substrate 1 is viewed from first side SI under white light. Different examples for second personalized image 8 will be described in the following. In any case, it will be appreciated by the skilled person that the expression “personalized image” as used herein means that such a personalized image includes a specific image or other information that is associated with an individual such as a holder of security document 10. Accordingly, an image that is the same for at least a plurality of security documents, such as a watermark or another pattern that is visible whenviewed under UV light, is not to be considered as a personalized image, because it is the same for at least a plurality of such security documents. Further, as will be described in more detail in the following, the expression “formed at a position that corresponds to laser-engravable material layer 6” is to be understood such that second personalized image 8 is either formed in or on laser-engravable material layer 6, or overlaps the same when viewed along thickness direction d.

[0024] Fig. 3 shows a first exemplary configuration of security feature 3a in accordance with the present disclosure. In the embodiment shown in Fig. 3, first personalized image 5 is a negative of a portrait of a holder of security document 10, and is formed by laser engraving in first surface 6a of laser- engravable material layer 6 in the above-described manner. For example, in the Mirage feature, the region surrounding the portrait of the holder is processed by the laser to obtain a golden color, whereas the image features are formed using different laser powers to obtain different colors ranging from an initial dark blue to a lighter blue, silver, and the like. This is shown in the leftmost image in Fig. 3.

[0025] As shown in the second image from the left in Fig. 3, in the present embodiment, second personalized image 8 is laser-engraved in second surface 6b of laser-engravable material layer 6 opposite to first surface 6a of the same. In the example shown in Fig. 3, second personalized image 8 includes information associated with the holder of security document 10, for example, a date of birth. In other embodiments, a name of the holder of security document 10, a place of birth, and the like can be included in second personalized image 8. In the second image from the left in Fig. 3, second personalized image 8 is also formed as a negative in second surface 6b of laser-engravable material layer 6. However, as shown in the third image in Fig. 3, in other embodiments, second personalized image 8 also can be formed as a positive image, in other words, the information included in second personalized image 8 can be engraved into laser- engravable material layer 6, resulting in a color change of the part of the second surface 6b including the information.

[0026] In other exemplary embodiments, as shown in the rightmost image in Fig. 3, second personalized image 8 may include a first portion 8a engraved as one of a negative image and a positive image in laser-engravable material layer 6, and a second portion 8b engraved as another one of the negative image and the positive image in laser-engravable material layer 6. In particular, first portion 8a and second portion 8b may be aligned with and transitioning into each other, as shown in Fig. 3. It is evident that use of such a combination of a negative image and a positive image including information that is personalized further increases the security of security feature 3a including laser-engraved first and second personalized images 5 and 8.

[0027] Fig. 4 shows another configuration of laser-engravable material layer 6 in accordance with the present disclosure. As shown in Fig. 4, laser- engravable material layer 6, which has first and second personalized images 5, 8 formed on opposite surfaces 6a, 6b of the same, when viewed from second side S2 of security document 10 under white light, has a size that is different from a size of laser-engravable material layer 6 when viewed from first side SI under white light. In other words, an area of second surface 6b of laser-engravable material layer 6, in which an image can be laser engraved, is different from an area of first surface 6a of laser-engravable material layer 6 in which an image can be laser engraved. For example, as indicated by dashed lines in Fig. 4, an opaque cover layer 12 covering part of laser-engravable material layer 6 may be provided on one of first side SI and second side S2. In the example shown in Fig. 4, opaque cover layer 12 is provided on first side SI to cover part of the underlying laser-engravable material layer 6.

[0028] As shown in Fig. 4, with such an asymmetric configuration, second personalized image 8, for example, a portrait of the holder of security document 10, can have a same appearance as first personalized image 5, but differ from the same in at least one of a size, an orientation, or an aspect ratio. In the example shown in Fig. 4, second personalized image 8 is rotated clockwise with respect to first personalized image 5.

[0029] Fig. 5 shows a security feature 3b in accordance with a second embodiment of the present disclosure. Security feature 3b differs from security feature 3a described above in that a watermark 19 formed in a layer 18 of substrate 1 on the second side S2 of laser-engravable material layer 6 and overlapping at least in part laser-engravable material layer 6 when viewed along thickness direction d is provided. Watermark 19 is visible when substrate 1 is viewed from second side S2 under white light and / or when substrate 1 is viewed from first side SI against white light (i.e., in transmission under normal lighting conditions). Again, it will be appreciated that the arrangement of the layers of substrate 1 shown in Fig. 5 is only exemplary, and that one or more additional protective layers can be provided on top of first layer 16 and / or below layer 18. Likewise, the intermediate layers that are shown in Fig. 5 may be omitted, or additional security features, such as features including UV-sensitive inks, may be provided in said intermediate layers.

[0030] Fig. 6 shows security feature 3b of Fig. 5, in particular, an appearance of security feature 3b when viewed from first side SI under white light (left side in Fig. 6), and an appearance of security feature 3b when viewed from second side S2 under white light (right side in Fig. 6). It is evident that, when security document 10 including security feature 3b is viewed from second side S2 under white light, both watermark 19 and second personalized image 8 can be seen. Likewise, although this is not shown in Fig. 6, when security document 10 is viewed from first side SI in transmission, watermark 19 can also be seen in addition to first personalized image 5. In this manner, the security of security document 10 can be further increased. Here, it will be appreciated that, in some embodiments, part of second personalized image 8 may be covered by watermark 19. For example, watermark 19 may be formed prior to laser engraving of second personalized image 8 by printing the same onto a surface of one of the internal layers of substrate 1, for example, by offset printing or the like.

[0031] Although in the above examples second personalized image 8 includes either image information such as a portrait of a holder, or additional information (personalized data) such as name, date of birth, or the like, it will be appreciated that, in other embodiments, second personalized image 8 may include a combination of such image information and additional information. For example, second personalized image 8 may include an image such as a portrait of the holder of security document 10, and in said image the further information such as a name (or a repetition of the name and the like) may be formed as part of the image (i.e., using the same process for forming the image).

[0032] Additionally, in the above examples, it is described that second personalized image 8 is formed by laser engraving in second surface 6b of laser- engravable material layer 6. However, in other embodiments, which will be described in the following, second personalized image 8 is not a laser-engraved image, but is instead printed onto substrate 1, for example, by ink-jet printing, preferably as a full color image. Also in this case, however, second personalized image 8 is formed at a position that corresponds to laser-engravable material layer 6, i.e., at a position overlapping laser-engravable material layer 6. As such, as explained above, the expression “a position that corresponds to the laser- engravable material layer” as used herein includes both the case in which second personalized image 8 is formed in an opposite surface of laser-engravable material layer 6, and the case in which second personalized image 8 is printed onto substrate 1 at a position such that it overlaps with laser-engravable material layer 6.

[0033] Fig. 7 shows several configurations of an exemplary security feature 3a or 3b including a combination of a laser-engraved image and a printed image. The left side of Fig. 7 again shows first personalized image 5, which is laser-engraved in first surface 6a of laser-engravable material layer 6. The second image in Fig. 7 shows second personalized image 8, which is formed on substrate 1 of security document 10 by printing, for example, as a full color image having gradually changing colors and including additional information such as a date ofbirth of the holder of security document 10. Here, it will be appreciated that second personalized image 8 can be formed by printing on any one of the layers of substrate 1 arranged below first layer 16 in which laser-engravable material layer 6 is provided. In some embodiments, for example, second personalized image 8 can be formed directly on first layer 16. In other embodiments, however, second personalized image 8 can be formed on a bottom layer of substrate 1, for example, layer 18 shown in Fig. 5. Here, it will be appreciated that any known techniques can be used to print second personalized image 8, for example, ink-jet printing, D2T2 (thermal transfer) printing, and the like.

[0034] While the second image in Fig. 7 shows an example in which second surface 6b of laser-engravable material layer 6 has been fully processed by the laser, i.e., has completely changed its color from the initial color (such as blue) to the color associated with maximum laser power (for example, golden), in other embodiments, as shown in the third image of Fig. 7, second surface 6b of laser-engravable material layer 6 may not be processed, i.e., may still have its initial color (in the example, blue). As shown in the rightmost image of Fig. 7, the security can be further enhanced by partially processing second surface 6b of laser-engravable material layer 6, for example, resulting in a processed portion and an unprocessed portion arranged next to each other. Again, second personalized image 8 can smoothly transition from the processed portion to the unprocessed portion of second surface 6b. The above examples of Fig. 7 may be considered as a (further) variable watermark provided on the second side S2 of laser-engravable material layer 6 including first personalized image 5.

[0035] In yet another example, which is not shown in the figures, second personalized image 8 may be formed as a full color portrait of the holder of security document 10 on the second side S2 of laser-engravable material layer 6. Also in this manner, a variable watermark can be obtained.

[0036] In other embodiments, the above-described second personalized image 8 being laser-engraved in second surface 6b may be combined with a further personalized image formed by printing, for example, on second side S2.

[0037] Further, while in the above examples second personalized image 8 is printed onto substrate 1 on the second side S2 of laser-engravable material layer 6, in other embodiments, second personalized image 8 can also be formed on the first side SI of laser-engravable material layer 6, as shown in Fig. 8. In such an example, second personalized image 8 partially covers first surface 6a of laser-engravable material layer 6. For example, as shown in Fig. 8, second personalized image 8 may at least partially surround first personalized image 5. Additionally, as also shown in Fig. 8, water mark 19 may again be provided, for example, in layer 18 shown in Fig. 5.

[0038] Additionally or as an alternative, as also shown in Figs. 5 and 8, security feature 3b may further include a varnish 20, preferably a transparent or translucent varnish, provided on a surface of substrate 1 on first side SI (or second side S2) of laser-engravable material layer 6. Varnish 20 may form a third personalized image 23 (or second personalized image 8) when viewed under white light, for example, from first side SI. For example, varnish 20 may be applied such that it imparts a glossy effect when security document 10 is viewed from first side SI under white light. In this manner, additional personalized information can be included in security feature 3b, and the security can be increased even further.Industrial applicability

[0039] With the above-described configurations, the security of personalized security document 10 is further increased, because not only a single personalized image is provided, but instead one or more additional personalized images can form part of the security features described herein.

[0040] An exemplary method of manufacturing personalized security document 10 is described in the following. In a first step, substrate 1 having first side SI and second side S2 opposite to first side SI in thickness direction d of substrate 1 is provided. Substrate 1 includes laser-engravable material layer 6 exhibiting a color-change effect upon irradiation with laser light.

[0041] Security feature 3 is formed in substrate 1 such that security feature 3 extends through at least part of substrate 1 along thickness direction d. In particular, security feature 3 is formed by laser engraving a first personalized image 5 in first surface 6a of laser-engravable material layer 6 by irradiating laser light onto the same from first side SI. First personalized image 5 is visible when substrate 1 is viewed from first side SI under white light. Additionally, second personalized image 8 is formed at a position that corresponds to laser-engravable material layer 6. Second personalized image 8 is visible when substrate 1 is viewed from one of first side SI and second side S2 under white light.

[0042] For example, as shown in Fig. 9, security document 10 may include laser-engravable material layer 6 disposed on an inner layer 14 of substrate 1 in the above-described manner. First personalized image 5 is formed by irradiating laser light LI from first side SI to laser engrave first personalized image 5 in first surface 6a of laser-engravable material layer 6. Simultaneously or prior to or after forming first personalized image 5, second personalized image 8 is formed by irradiating laser light L2 from second side S2 to form second personalized image 8. Here, it will be appreciated that laser light LI and laser light L2 may be the same laser light, i.e. have the same wavelength.

[0043] As described above, in an alternative or in addition, second personalized image 8 may be formed by printing onto substrate 1 from one of first side SI and second side S2, for example, by ink-jet printing, preferably as a full color image.

[0044] It will be readily apparent to the skilled person how, with the above exemplary methods and appropriate modifications of the same, a personalized security document 10 according to the present disclosure, as described above, can be obtained.

[0045] It will be appreciated that the foregoing description provides examples of the disclosed systems and methods. However, it is contemplated that other implementations of the disclosure may differ in detail from the foregoing examples. All references to the disclosure or examples thereof are intended toreference the particular example being discussed at that point and are not intended to imply any limitation as to the general disclosure.

[0046] Recitation of ranges of values herein are merely intended to serve as a shorthand method for referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All method steps described herein can be performed in any suitable order, unless otherwise indicated or clearly contradicted by the context.

[0047] Although the preferred embodiments of the present disclosure have been described herein, improvements and modifications may be incorporated without departing from the scope of the following claims.

Claims

Claims1. A personalized security document (10) comprising: a substrate (1) having a first side (SI) and a second side (S2) opposite to the first side in a thickness direction (d) of the substrate (1); and a security feature (3; 3a; 3b) formed in the substrate (1) and extending through at least part of the substrate along the thickness direction (d), wherein the security feature (3; 3a; 3b) includes: a laser-engravable material layer (6) including a first personalized image (5) laser engraved in a first surface (6a) of the same, the laser-engravable material layer (6) exhibiting a color-change effect upon irradiation with laser light, the first personalized image (5) being visible when the substrate (1) is viewed from the first side (SI) under white light; and a second personalized image (8) formed at a position that corresponds to the laser-engravable material layer (6), the second personalized image (8) being visible when the substrate (1) is viewed from one of the first side (SI) and the second side (S2) under white light.

2. The security document of claim 1, wherein the second personalized image (8) is laser engraved in a second surface (6b) of the laser- engravable material layer (6) opposite to the first surface (6a) of the same, the second personalized image (8) being visible when the substrate (1) is viewed from the second side (S2) under white light.

3. The security document of claim 2, wherein the second personalized image (8) includes a first portion (8a) engraved as one of a negative image and a positive image in the laser-engravable material layer (6), and a second portion (8b) engraved as another one of the negative image and the positive image in the laser-engravable material layer (6), the first portion (8a) and the second portion (8b) being aligned with and transitioning into each other.

4. The security document of any one of claims 1 to 3, wherein the laser-engravable material layer (6), when viewed from the second side (S2) under white light, has a size that is different from a size of the laser- engravable material layer (6) when viewed from the first side (SI) under white light.

5. The security document of claim 4, further comprising an opaque cover layer (12) covering part of the laser-engravable material layer (6) on one of the first side (SI) and the second side (S2).

6. The security document of claim 4 or 5, wherein the second personalized image (8) has a same appearance as the first personalized image (5), but differs from the same in at least one of a size, an orientation, or an aspect ratio.

7. The security document of any one of claims 1 to 6, further comprising a watermark (19) formed in a layer (18) of the substrate (1) on the second side (S2) of the laser-engravable material layer (6) and overlapping at least in part the laser-engravable material layer (6) when viewed along the thickness direction, the watermark (19) being visible when the substrate (1) is viewed from the second side (S2) under white light and / or when the substrate (1) is viewed from the first side (SI) against white light.

8. The security document of claim 1, wherein the second personalized image (8) is printed onto the substrate (1), for example, by inkjet printing, preferably as a full color image.

9. The security document of claim 8, wherein the second personalized image (8) partially covers a second surface (6b) of the laser- engravable material layer (6) opposite to the first surface (6a) of the same,wherein a visible portion of the second surface (6b) has been fully or partially processed by the laser light, or has not been processed by the laser light.

10. The security document of claim 8, wherein the second personalized image (8) partially covers the first surface (6a) of the laser- engravable material layer (6), preferably wherein the second personalized image (8) at least partially surrounds the first personalized image (5).

11. The security document of claim 10, further comprising a varnish (20), preferably a transparent or translucent varnish, provided on a surface of the substrate (1) on the first side (SI) or the second side (S2) of the laser-engravable material layer (6), the varnish forming a third personalized image (23) when viewed under white light.

12. The security document of any one of claims 1 to 11, wherein the first personalized image (5) is a portrait of a holder of the security document (10), and the second personalized image (8) includes information associated with the holder of the security document (10), for example, a name, a date of birth, a place of birth, and the like.

13. A method of manufacturing a personalized security document (10), comprising: providing a substrate (1) having a first side (SI) and a second side (S2) opposite to the first side in a thickness direction (d) of the substrate (1), the substrate including a laser-engravable material layer (6) exhibiting a color-change effect upon irradiation with laser light; and forming a security feature (3; 3a; 3b) in the substrate (1), the security feature (3; 3a; 3b) extending through at least part of the substrate along the thickness direction (d), by laser engraving a first personalized image (5) in a first surface (6a) of the laser-engravable material layer (6) by irradiating laser light onto the samefrom the first side (SI), the first personalized image (5) being visible when the substrate (1) is viewed from the first side (SI) under white light, and forming a second personalized image (8) at a position that corresponds to the laser-engravable material layer (6), the second personalized image (8) being visible when the substrate (1) is viewed from one of the first side (SI) and the second side (S2) under white light.

14. The method of claim 13, wherein the second personalized image (8) is formed by laser engraving in a second surface (6b) of the laser- engravable material layer (6) opposite to the first surface (6a) of the same, the second personalized image (8) being visible when the substrate (1) is viewed from the second side (S2) under white light.

15. The method of claim 13, wherein the second personalized image (8) is formed by printing onto the substrate (1) from one of the first side (SI) and the second side (S2), for example, by inkjet printing, preferably as a full color image.

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