WO2018020224A1

WO2018020224A1 - Anti-counterfeit image

Info

Publication number: WO2018020224A1
Application number: PCT/GB2017/052156
Authority: WO
Inventors: Jose Guadalupe CALIXTO GORTAREZ; Christopher James GODDARD
Original assignee: Nautilus (Gb) Limited
Priority date: 2016-07-26
Filing date: 2017-07-24
Publication date: 2018-02-01
Also published as: GB2552778A; GB2552778B; GB201612929D0

Abstract

A product comprising a first substrate having a first visual feature provided on a first surface thereof, the first substrate being at least partially transparent. The product further comprises a second surface having a second visual feature provided thereon. the first and second visual features configured such that overlapping of the first and second surfaces such that the first substrate is between the first and second visual features, causes the first and second visual features to optically interact to reveal a hidden image, the hidden image comprising a first portion having a first visual property and a second portion having a second visual property, and further configured such that the first and second properties undergo modification when the hidden image is viewed at different angles.

Description

Anti-Counterfeit Image

Technical Field

The present invention relates to products and method for their production, which may in some particular embodiments be used for providing an anti-counterfeit image.

Background

Counterfeiting of products is a serious problem for both producers of such products and the general public. Counterfeit products are often not as well made as the genuine article and can sometimes even be hazardous, particularly if they contain electronics, as they will not likely conform to any recognised safety standards. Counterfeiting of Government issued documents, such as passports and money, is also a serious problem.

One way to help prevent counterfeiting is to provide optical security features on products or documents to indicate that they are authentic. Such optical security features are difficult to reproduce and may be referred to as anti-counterfeit images. The term "anti-counterfeit image" is used herein to denote any image that has a recognisable meaning, to either a human or machine, but that is difficult to reproduce. Examples of anti-counterfeit images include images contained in holograms or watermarks. The image may be of an object, such as a dove, as seen on Visa credit cards. The image may comprise patterns that are recognisable by a person or computer, such as a bar code or Q-code. Alternatively, the image may comprise letters or numbers, and may spell a word. Such images may be easily recognisable by a human, and can provide a quick visual confirmation as to whether an article containing an anti-counterfeit image is genuine.

Anti-counterfeit images are routinely used in articles such as money, passports, certificates, official documents, etc. Due to the difficulty in reproducing anti-counterfeit images, their use helps to prevent unauthorised third parties from copying products which contain anti-counterfeit images. For example, a counterfeiter may find it relatively easy to generally reproduce an article, but would find it very difficult to reproduce the anti-counterfeit image. Lack of the anti-counterfeit image on the article, or a poor copy of the anti-counterfeit image, indicates to an end user that the article is likely not genuine.

One method of producing an anti-counterfeit image is to hide an image in a pattern, which can only be viewed when a user uses an optical decoder. It is known, for example, to print a line pattern on a surface. The line pattern generally comprises a series of uniform parallel lines. However, some sections of some of the lines contain slight deviations from the uniform parallel lines. Such deviations (or modulations) in the line pattern encode the hidden image. When the line pattern is viewed with the naked eye, the image hidden in the line pattern cannot be recognised or resolved. However, when the image is viewed through a suitable optical decoder, the hidden image becomes visible such that it may be recognised by a human or machine.

Figure 1 shows a cross sectional view of a known optical decoder 1. The decoder 1 is formed from a transparent substrate, and has a uniform series of raised convex portions 2 so as to produce a series of parallel grooves 3. The frequency of the grooves 3, i.e. the number of grooves per unit length, corresponds to the frequency of the lines used in the line pattern. The raised convex portions 2 have generally curved surfaces 4 between the grooves 3, and are arranged such that when placed over the line pattern, light is refracted from the line pattern in different directions. The modulation of the line pattern is chosen to work with a specific optical decoder 1 , such that when a user views the line pattern through the optical decoder 1 , the light from the pattern is refracted in such a way as to produce a recognisable pattern, such as a letter or image of an object.

Manufacturing anti-counterfeit images can be expensive and time consuming. Therefore, there exists a need for an easier to produce anti-counterfeit image, which is still difficult to reproduce by unauthorised third parties. Summary of the Invention

According to a first aspect of the present invention, there is provided a product. The product comprises a first substrate having a first visual feature provided on a first surface thereof, the first substrate being at least partially transparent. The product further comprises a second surface having a second visual feature provided thereon. The first and second visual features are configured such that overlapping of the first and second surfaces such that the first substrate is between the first and second visual features, causes the first and second visual features to optically interact to reveal a hidden image, the hidden image comprising a first portion having a first visual property and a second portion having a second visual property, and further configured such that the first and second properties undergo modification when the hidden image is viewed at different angles.

Advantageously, the product does not rely on the refraction of light via a decoder to produce a hidden image. The second surface may be arranged such that the first and second visual features are distinguishable from the second surface. In an embodiment the second surface may be a surface of a material, the material comprising any of a transparent, translucent or opaque material. Overlapping of the first and second surfaces may be achieved by arranging the first and second surfaces to be parallel to one another. Overlapping of the first and second surfaces may be taken to include overlapping of the first and second surfaces such that the first and second visual features overlap. The overlap may defined such that the first and second surfaces (or first and second visual features) overlap when viewed from one or more angles.

In an embodiment the modification may be an inversion of the first and second visual properties. In an embodiment the first and second visual property may be any one of a colour, contrast, or shape.

In an embodiment the first visual property arises as a result of at least a combination of a background and the first visual feature and the second visual property arises as a result of at least a combination of the first visual feature and the second visual feature, and wherein when viewed from a second angle, the first visual property arises as a result of at least a combination of the first visual feature and the second visual feature and the second visual property arises as a result of at least a combination of the background and the first visual feature.

For example, the background may be a portion of the second surface which does not comprise the second visual feature. As an example, if the second visual feature comprised a series of printed lines, separated by a series of blank spaces, or gaps, the background may be defined as the portion of the second surface comprising the blank spaces, or gaps, between the printed lines. In an embodiment the first visual feature may be applied to the first surface and the second visual feature may be applied to the second surface using a method of printing. Optionally, the method of printing may comprise any one of an ink jet, laser jet, flexographic, lithographic, screen, gravure, intaglio, or any other suitable printing method.

In an embodiment the second surface may be a surface of the first substrate. Optionally, the second surface may be located on an opposite side of the first substrate than the first surface. For example, the substrate may by transparent material having at least two surfaces which may be parallel to one another, where the first visual feature is applied to one of the at least two surfaces and the second visual feature is applied to the other of the at least two surfaces.

In an embodiment, the product may further comprise a second substrate, wherein the second substrate comprises the second surface. An example of such an embodiment may be where the first substrate may comprise a transparent material and the second substrate comprises a non-transparent material. For example, the second substrate could be part of a document, such as a passport or boarding pass, and may comprise paper. The first and second substrates may be coupled into a single document, and arranged such that by folding the document, the first and second visual features are made to overlap. Alternatively, the first and second substrates may be separate, uncoupled, substrates.

In an embodiment the first substrate has a width defining a distance between the first and second surfaces. In such an embodiment, the first substrate may be transparent. For example, when the first and second visual features are made to overlap, the first substrate may be arranged to provide a distance between the first and second visual features. Optionally, the distance is less than 0.5mm.

Optionally, the first and/or second visual feature may comprise any of a plurality of lines and/or dots. That is, both the first and second visual features may comprise lines, dots, or a combination of both. The lines and/or dots of the first visual feature may optically interact with the lines and/or dots of the second visual feature to reveal the hidden image. Optionally, one or both of the first and second visual features may comprise a modulation. The modulation may encode the hidden image.

In an embodiment, the first visual feature may comprise a uniform series of parallel lines separated by a series of gaps. Optionally, the distance between each of the uniform series of parallel lines is less than 0.5 mm. The second visual feature may comprise a modulated series of lines separated by a series of gaps. The modulation may be provided by deviating one or more portions of one or more of the lines of the second visual feature. That is, the lines of the second visual feature may comprise a uniform series of parallel lines, where one or more portions of the one or more of the lines are deviated. The un-deviated portions of the lines of the second visual feature may comprise the same distance between each line as the distance between each of the uniform series of parallel lines of the first visual feature. The deviation may, for example, by a shift of one or more of the lines. The shift may be in a perpendicular direction to a direction of the one or more of the lines. The shift may be less than the distance between each of the uniform series of parallel lines of the first visual feature. In an embodiment, the distance between the lines and/or dots is less than 0.5mm. For example, if the first and second visual features comprise a series of parallel lines, the distance between sections of those lines not containing any deviations may be less than 0.5mm. In a second aspect of the present invention, there is provided a product comprising a first substrate having a first visual feature provided on a first surface thereof, the first substrate being at least partially transparent; and arranged such that when configured so as to overlap a second surface having a second visual feature provided thereon, and where the first substrate is between the first and second visual features, the first and second visual features optically interact to reveal a hidden image, the hidden image comprising a first portion having a first visual property and a second portion having a second visual property, and further arranged such that the first and second properties undergo modification when the hidden image is viewed at different angles. Embodiments and optional features of the first aspect may be used with the second aspect. Brief Description of Drawings

Embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, in which:

Figure 1 illustrates a cross section of a prior art decoder;

Figure 2A illustrates a first and second visual feature;

Figure 2B illustrates a composite of the first and second visual features of Figure 2A; Figure 3 illustrates a cross section of a substrate comprising the first and second visual features of Figure 2A;

Figure 4 illustrates an exploded view of a substrate comprising the first and second visual features of Figure 2A;

Figures 5A illustrates the composite image of Figure 2B when viewed at a first angle showing a hidden image;

Figures 5B illustrates the composite image of Figure 2B when viewed at a second angle showing the hidden image having undergone an inversion;

Figure 6 is an image of an embodiment at a first angle;

Figure 7 is an image of the embodiment of Figure 6 at a second angle;

Figure 8A illustrates a schematic of an article containing the first and second visual features of Figure 2A;

Figure 8B illustrates a cross section through the article of Figure 8A;

Figure 9 illustrates a schematic of an article containing the second visual features of

Figure 2A, and a separate decoder containing the first visual feature of Figure 2A;

Figure 10 illustrates the article of Figure 9, with the decoder being used to decode a hidden image;

Figure 1 1 illustrates an example visual feature; and

Figure 12 is a flow diagram of a method of producing an anti-counterfeit image. Detailed Description

With reference to the Figures 2A to 1 1 , there is now described an optical system for producing a hidden image. Advantageously, the optical system does not rely on the refraction of light via a decoder to produce the hidden image. Instead, the optical system relies on the optical interaction of two visual features to produce the hidden image. Figure 2A shows an exaggerated view of a first visual feature 5 and a second visual feature 6. The first visual feature 5 comprises a uniform series of parallel lines 5a separated by a series of gaps. The second visual feature 6 comprises a uniform series of parallel lines 6a separated by a series of gaps, and where some sections of the lines 6a have been modulated, so as to provide deviations 6b from the lines 6a. The deviations 6b are created by shifting a section of the lines 6a perpendicular to the direction of the lines 6a to create an offset between the lines 6a and the deviations 6b. Note that the deviations 6b need not be continuous with the parallel lines 6a, i.e. the deviations 6b could be formed as separate lines which are offset from the lines 6a. While the first visual feature 5 is shown as a lighter shade of grey than the second visual feature 6, this is for illustration purposes. The first and second visual features 5, 6 may be the same colour, or may be different colours.

By arranging the first visual feature 5 to overlap with the second visual feature 6 (or vice versa), an anti-counterfeit image 7 is obtained as shown in Figure 2B. The anti- counterfeit image 7 is a composite of the first and second visual features 5, 6, and, in the present example, is set against a white backdrop. It will be appreciated that the backdrop may be opaque or transparent, and may be any colour, such that the first and second visual features 5, 6 are distinguishable from the backdrop. The optical interaction of the lines 5a, 6a and deviations 6b produces a hidden image. From the view point of Figure 2B, the hidden image has a first section 7a formed from the interaction of lines 5a and deviations 6b, which is darker than a second, background, section 7b which is formed from the interaction of lines 5a and 6a (where the horizontal dotted lines divide the sections). In other words, the hidden image is a stripe 7a set against a background section 7b, the stripe 7a running perpendicular to the uniform series of parallel lines 5a, 6a.

A transparent gap is provided between the first and second visual features 5, 6 (i.e. there is a distance between the plane of the first visual feature 5 and the plane of the second visual feature 6). In an embodiment, this may be provided by a transparent substrate 8, where the first and second visual features are applied to either side of the substrate 8. Figure 3 shows such an arrangement in cross section (not to scale). The substrate 8 has a width W, defining the distance between the first and second visual features 5, 6. In a preferred embodiment, the width W may be less than 0.5mm. Figure 4 shows an exploded view of the embodiment shown in Figure 3, where the first and second visual features 5, 6 are applied to either side of the transparent substrate 8. For ease of depiction, the first and second visual features 5, 6 are shown as a uniform blocks, rather than being composed of individual lines as described above.

By providing a transparent gap of width W between the first and second visual features 5, 6, appropriate angling of the substrate 8 will lead to the lines 5a, 6a, of the first and second visual features 5, 6 lining up such that the background section 7b of the anti- counterfeit image 7 appears darker than the stripe 7a of the anti-counterfeit image 7, or vice versa. In other words, angling of the anti-counterfeit image 7 from one angle to another leads to a modification of the hidden image contained within the anti- counterfeit image 7. In the case shown in Figure 2B, this modification is a contrast inversion of the hidden image, where the stripe 7a becomes lighter than the background section 7b (and vice versa).

This is shown in Figures 5A and 5B. Figure 5A shows the anti-counterfeit image 7 when angled to show the stripe 7a as a dark strip across the central portion of the hidden image, with the background section 7b forming a lighter background. The optic distance, i.e. the distance between the first and second visual features 5, 6 is also highlighted. When viewed at the angle as shown in Figure 5A, the parallel lines 5a of the first visual feature 5 are made to line up with the parallel lines 6a of the second visual feature 6, whereas the deviations 6b of the second visual feature 6 do not line up with the lines 5a of the first visual feature 5. In other words, assuming that the backdrop is white and the visual features 5, 6 are black, the average colour of the background section 7b, formed from the lines 5a, 6a and the backdrop, is grey, and the average colour of the stripe 7a, formed from the lines 5a and deviations 6b, is a black.

Figure 5B shows the anti-counterfeit image 7 when angled at a different angle, and shows the stripe 7a as a grey colour against the background section 7b which is black. In this case, the parallel lines 5a of the first visual feature 5 do not line up with the parallel lines 6a of the second visual feature 6, whereas the deviations 6b of the second visual feature 6 do line up with the lines 5a.

While the examples shown in Figures 5a and 5b are set against the white backdrop of the page, it will be appreciated that the backdrop to which the anti-counterfeit image is to be applied does not need to be white. For example, if the backdrop is yellow, and the lines 5a, 6a, 6b of the first and second visual features are blue, then the anti- counterfeit image will produce a hidden image having a stripe which looks blue against a green background (where the mixing of the blue lines and yellow backdrop produces a green background when viewed from a distance). These colours will be inverted when the anti-counterfeit image is viewed from a different angle, i.e. the stripe will appear green on a blue background. There is a relationship between the width of the lines 5a, 6a, the width of the deviations 6b, the width of the gaps between the lines 5a, 6a and deviations 6b, and the width W of the gap between the first and second visual features. The width of the gaps between the lines 5a, 6a are dependent on the line frequency (i.e. the number of lines per unit length), which may be limited by the manufacturing capabilities, such as the resolution of a printer used to print the lines 5a, 6a. The width of the lines 5a, 6a may be equal to the width of the gaps between the lines 5a ,6a, or may vary between 10% and 90% of width of the gaps between the lines 5a, 6a. The width of the gaps between the lines 5a, 6a can be chosen with respect to the intensity of the deviations 6b. The larger the deviations 6b from lines 6a, the more distance between the lines 5a, 6a will be required to create a strong effect. Depending on the specific arrangement of the lines, deviations and gap, the hidden image can undergo inversion multiple times when angled through 180 degrees. For example, the hidden image may undergo inversion four times when angled through 180 degrees. The hidden image in the anti-counterfeit image 7 described above is a simple stripe running parallel to the lines 5a, 6a of the first and second visual features 5, 6. This was achieved by providing simple deviations 6b in the lines 6a of the second visual feature 6. It will be appreciated that by providing more complex deviations of the lines, a more complex image may be produced when the first and second visual features 5, 6 are made to overlap. For example, the hidden image may be a pattern that spells out a word, or resembles an object, such as a company logo. It will also be appreciated that gradients and vignettes can be hidden within the hidden image.

Referring to Figures 6 and 7, an image of an anti-counterfeit image 20 according to an embodiment of the invention is shown. The first and second visual features 5, 6 of the anti-counterfeit image 20 comprise dark lines, are separated by a transparent substrate as described above, and are viewed against a white backdrop. The second visual feature 6 of the anti-counterfeit image 20 has been modulated such that a hidden image appears as the word "OK" 21 on a background 22. In Figure 6, the angle of the photograph generally shows the word "OK" 21 to be lighter than the background 22. In Figure 7, the angle of the photograph has been changed, such that the word "OK" 21 is generally darker than the background 22. In other words, as the viewing angle has changed, the contrast of the word "OK" 21 and the background 22 has been inverted.

While the above example has been described using visual features that are comprised of uniform parallel lines, it will be appreciated that the other visual features may be used to achieve the same effect. For example, the first visual feature 5 may instead comprise a uniform dot screen, such as a series of dots arranged in a uniform manner, and the second visual feature may also comprise a uniform dot screen, but where the position, shape, or size of some of the dots are modulated to provide deviations. Alternatively, lines and dots may be combined, for example, the first visual feature 5 may comprise a uniform series of parallel lines, and the second visual feature may comprise a uniform dot screen, but where the position, shape, or size of some of the dots are modulated to provide deviations. The substrate 8 may be formed from a single piece of transparent material, such as a plastic film, or may be built up using multiple transparent layers. The first and second visual features 5, 6 may be obtained by depositing a material onto either side of the substrate 8, or may be made to appear on the substrate 8 using any other technique. For example, ink may be deposited by printing directly onto the substrate 8 using an ink jet printer. Alternatively, the first and second visual features 5, 6 may be generated using further types of printing, such as laser jet, flexographic, lithographic, screen, gravure, or intaglio.

Once the first visual feature 5 and the second visual feature 6 have been applied to the substrate 8, the substrate 8 may then be applied to an article, such as a passport, in order to demonstrate that the article is genuine.

In an alternative embodiment, the first visual feature 5 may be applied to a non- transparent surface and the second visual feature 6 may be applied to a transparent surface. For example, Figure 8A shows a document 9, which could be a paper document such as a passport or boarding pass, and which has a fold 10 separating a first side 11 and a second side 12 of the document 9. The fold 10 may be, for example, a crease in the document 9, or may be a spine if the document 9 is a booklet. The second side 12 has a region that has been cut out to form a viewing window 13, and a transparent film 14 placed over the viewing window 13. The first visual feature 5 is applied to the first side 11 of the document 9, and the second visual feature 6 is applied to the transparent film 14. In particular, the second visual feature 6 is applied to a side of the transparent film 14 facing away from the side on which the first visual feature 5 is applied. This arrangement is more clearly shown in Figure 8B, which shows a cross section though the document 9 along the dotted line A of Figure 8A. In Figure 8B the transparent film 14 has been shown as a dotted line to indicate its transparency. Again, for simplicity, the first and second visual features 5, 6 are shown as uniform blocks, and the figure is not to scale. For example, it will be appreciated that the width of document 9, and the first and second visual features have been exaggerated for illustration. Figure 8B also shows two curved arrows, indicating the direction in which each side 1 1 , 12 of the document 9 is folded to bring the visual features 5, 6 together to overlap. The transparent film 14 may, for example, be a plastic film, or any other suitable substrate (such as plasticized corn starch).

The positioning of the first visual feature 5 and second visual feature 6 is such that when the document 9 is folder over, the viewing window 13 and therefore the second visual feature 6 lines up with and overlaps the first visual feature 5. Furthermore, as the second visual feature 6 is applied to the opposite side of the transparent film 14, the thickness of the transparent film 14 provides a distance between the planes of the two visual features 5, 6 so as to achieve inversion of the contrast or colour when the document is angled at different angles while being viewed through the viewing window 13.

In an alternative embodiment, only the second visual feature 6 is applied to an article to be protected and a separate decoder may be provided comprising the first visual feature 5. This arrangement is shown schematically in Figures 9 and 10.

A decoder 16 comprises a transparent substrate and has the first visual feature 5 applied to one side of the decoder 16. The first visual feature 5 may be printed directly onto the decoder 16, or may be printed onto a transparent sticker, which is then stuck to the decoder 16. In Figure 9, the first visual feature 5 is shown as comprising a series of uniform black parallel lines. The second visual feature 6 is also shown as comprising a series of uniform black parallel lines. It will be appreciated that the second visual feature 6 will also comprise a modulation in the lines (not shown) such as the type described above which encodes a hidden image. In order to determine if the article is genuine, a user places the decoder 16 over the second visual feature 6, with the side of the substrate containing the first visual feature 5 pointing away from the surface of the article 15 (i.e. pointing upward in Figure 9), such that the thickness of the decoder 16 provides a distance between the two planes of the first and second visual features 5, 6.

When the decoder 16 is appropriately placed, the first and second visual features 5, 6 optically interact so as to decode a hidden image encoded into the second visual feature 6, which, in the example shown in Figure 10, is depicted as a circle 17. The circle 17 is shown as white, and the surrounding area (i.e. the background) 17b of the circle 17 as black. The visual effect is exaggerated in Figure 10, but serves to highlight the contrast difference between the hidden image and the background when viewed at the angle portrayed. If the user were to change their viewpoint appropriately, the contrast of the hidden image would swap with the background 17b, such that the circle 17 would appear darker and the background 17b would appear lighter, as described above. While it has been described that the first visual feature is uniform, and the second visual feature contains the deviations, the skilled person will realise that this arrangement may be swapped, such that the second visual feature is uniform, and the first visual feature contains the deviations. Furthermore, while the optical system has been described using a uniform visual feature, and a modulated visual feature, it will be appreciated by the person skilled in the art that both visual features could contain deviations to a generally uniform pattern in order to produce the hidden image when the first and second visual features are arranged to overlap as described above.

While the deviations 6b have been described as deviated lines having the same thickness of as the lines 5a, 6a, the deviations may comprise any suitable deviation to create the effect. For example, the deviations 6b may comprise a deviation in the width of the line 6a. Different types of deviations may also be combined. An example of an alternative visual feature having two types of deviation is shown in Figure 1 1. A uniform series of lines 18 is shown, which have the general form of a wave. Some of the lines 18 have deviations from the uniform series which take the form of amplitude deviations 19a and offset deviations 19b. The amplitude deviations 19a are created by varying the thickness of the lines 18, and the offset deviations 19b are created by shifting a section of the lines 19b perpendicular to the direction of the lines 18 to create an offset between the lines 18 and the offset deviations 19b.

In some embodiments, the anti-counterfeit image may be incorporated into a sticker, having an adhesive layer on one or both sides. If the visual features are printed onto a side containing adhesive, this will reduce the overall surface area of adhesive, reducing the effectiveness of the sticker to stick to an article. Therefore, the arrangement of the visual features, such as the width of the lines or the gaps between the lines, may be chosen so as to not unduly reduce the effectiveness of the adhesive layer. In such situations, preferably 40% of the adhesive layer may be covered with the visual feature, leaving 60% of the adhesive exposed.

With reference to Figure 12, there is now described a method of manufacturing a product, such as the anti-counterfeit image 7.

At step SO data indicative of the characteristics of a hidden image to be produced are received. This data may be received by a customer who wants to use a hidden image in one of their products. The data may indicate what shape, wording, etc., that they would like to appear in the hidden image, and may also include details of how the hidden image should be modified when viewed at different angles, for example, contrast inversion, colour inversion, etc.

At step S1 the received data is used to generate second data corresponding to the first visual feature 5 and third data corresponding to the second visual feature 6.

At step S2 the first visual feature 5 is applied to a first surface of a substrate, such as the substrate 8 described above.

At step S3 the second visual feature 6 is applied to a second surface. The second surface may be a surface of the transparent substrate 8 opposite the first surface, as shown in Figures 3 and 4, or may be a surface on a different article as shown in Figures 8A to 10.

Further details may be taken into account when generating the second data and the third data, such as the thickness of the substrate to which the first and second visual features are to be applied, for example.

Embodiments of the invention have been described. Variations and modifications will suggest themselves to those skilled in the art without departing from the scope of the inventions as defined by the appended claims. Furthermore, separate embodiments that have been described may be combined with other embodiments described, or used separately.

Claims

CLAIMS:

1. A product comprising

a first substrate having a first visual feature provided on a first surface thereof, the first substrate being at least partially transparent;

a second surface having a second visual feature provided thereon;

the first and second visual features configured such that overlapping of the first and second surfaces such that the first substrate is between the first and second visual features, causes the first and second visual features to optically interact to reveal a hidden image, the hidden image comprising a first portion having a first visual property and a second portion having a second visual property, and further configured such that the first and second properties undergo modification when the hidden image is viewed at different angles.

2. A product according to claim 1 , wherein said modification is an inversion of the first and second visual properties.

3. A product according to any preceding claim, wherein the first and second visual property is any one of a colour, contrast, or shape.

4. A product according to any preceding claim, wherein, when viewed from a first angle, the first visual property arises as a result of at least a combination of a background and the first visual feature and the second visual property arises as a result of at least a combination of the first visual feature and the second visual feature; and wherein when viewed from a second angle, the first visual property arises as a result of at least a combination of the first visual feature and the second visual feature and the second visual property arises as a result of at least a combination of the background and the first visual feature.

5. A product according to any preceding claim, wherein the first and second visual features are applied to the first surface and the second surface using a method of printing.

6. A product according to claim 5, wherein the method of printing comprises any one of an ink jet, laser jet, flexographic, lithographic, screen, gravure, or intaglio printing method.

7. A product according to any preceding claim, wherein the second surface is a surface of the first substrate.

8. A product according to claim 7, wherein the second surface is located on an opposite side of the first substrate than the first surface.

9. A product according to any one of claims 1 to 6, further comprising a second substrate, wherein the second substrate comprises the second surface.

10. A product according to any preceding claim, wherein the first substrate has a width defining a distance between the first and second surfaces.

1 1. A product according to claim 10, wherein the distance is less than 0.5mm.

12. A product according to any preceding claim, wherein the first and/or second visual feature comprise any of a plurality of lines and/or dots.

13. A product according to claim 12, wherein a distance between the lines and/or dots is less than 0.5mm.

14. A product comprising

a first substrate having a first visual feature provided on a first surface thereof, the first substrate being at least partially transparent; and

arranged such that when configured so as to overlap a second surface having a second visual feature provided thereon, and where the first substrate is between the first and second visual features, the first and second visual features optically interact to reveal a hidden image, the hidden image comprising a first portion having a first visual property and a second portion having a second visual property, and further arranged such that the first and second properties undergo modification when the hidden image is viewed at different angles.