Detecting counterfeit DOVIDs.
Van Renesse is Chairman of the Optical Document Security conference and author of Optical Document Security (ISBN 1-58053-258-6).
Here I discuss three high security DOVIDs that have been produced by very different technologies and their corresponding counterfeits:
1. Image matrix and 2D/3D hologram recombination;
2. Blazed grating graphics;
3. Image element graphics;
The counterfeits discussed below were all made using dot matrix graphics. Typical for dot matrix holograms is that each individual dot consists of a uniform grating. Grating frequency and/or orientation may vary per dot.
Image Matrix Graphics and 2D/3D Hologram Recombination
Image matrix DOVIDs are composed of tiny, closely fitting pixels that can have various geometrical shapes, such as rectangles, parallelograms, hexagons and cross shapes, while each pixel can consist of various areas with different fringe frequencies and/or fringe orientations. Therefore, image matrix graphics differ from dot matrix graphics and systems like Kinemax, SecureText (Pacific Holographics, USA) or the Holographic Imagesetter (New Light Industries, USA) are not dot matrix systems.
An example is a Caykur tea label, produced by Light Impressions International, UK, (Figure 1, left). The image matrix consists of hexagonal pixels. A prominent animation--imploding and exploding microtext--is displayed by an 8 mm diameter image matrix feature area within a 24 mm diameter 2D/3D area. The counterfeit is seen in Figure 1, right.
When slightly tilting the label about a vertical axis, both the parallactic shift in the 2D/3D area and the exploding microtext (Figure 3) can be readily observed even under relatively diffuse illumination.
On first sight the dot matrix counterfeit looks surprisingly similar to the original. However, the exploding text animations are absent in the counterfeit and, moreover, the 2D/3D feature is reduced to a 2D feature without parallax. Therefore it is easy to establish in first line - or simple visual - inspection that the dot matrix feature is a counterfeit. Although dot matrix technology allows creating 2D/3D features, this is only possible with advanced dot matrix equipment.
Blazed Grating Graphics
Kinegrams (OVD Kinegram, Switzerland) typically feature the Diffractive Watermark[R], composed of gratings with an asymmetric sawtooth shaped cross section (blazed gratings). This feature displays an easily notable positive-to-negative swap on rotating it 180[degrees] in its own plane or, more practically, by tilting it between the +1st and -1st diffraction order about a horizontal axis. The advantage of this feature is that its positive-to-negative swap about the zero order can neither be created nor copied with common holographic techniques because these only generate gratings with symmetrical sinusoidal wave cross sections.
An example is the Dutch passport sticker for aliens. The outer ring of the image consists of demetallized diffractive rectangular spots that become smaller towards the perimeter. When tilted about a horizontal axis the +1st and -1st order display the positive-to-negative effect (Figure 4 - next page).
A dot matrix counterfeit of the Dutch passport sticker for aliens shows some similarity with the original (Figure 5), but the positive-negative image swap about the zero order is lacking and this unquestionably marks the dot-matrix feature as fake.
Apart from the counterfeit thus being very obvious as such on first line inspection, it is interesting to note that the counterfeit passport sticker contains a series of obvious spelling errors.
Image Element Graphics
Image element DOVIDs are composed of multiple diffractive alphanumerics and images, each consisting of a uniform grating. Grating frequency and/or orientation may vary per diffractive element. Examples are the Alpha-grams (Hologram Industries, France) on the higher denomination euro notes. On tilting these about a horizontal axis, three main features are observed: the face value and a doorway, while rainbow-coloured concentric circles of microtext explode and implode (Figure 6).
The dot matrix counterfeit also displays this threefold animation and on first sight the counterfeit appears to be very deceptive (Figure 7). However in the counterfeit the micro-text rainbow colours are considerably less prominent and the doorway only becomes visible after the microtext has disappeared. But, apart from these details, and contrary to the genuine feature, the counterfeit only displays this animation on tilting about a vertical axis. Therefore, as long as one knows how to tilt the feature for inspection, it is very easy to detect this counterfeit.
Making dot-matrix counterfeits that display these animations on tilting about a horizontal axis, is not a trivial matter.
Microscopic details of both the genuine image element structure and its counterfeit dot matrix structure are given in Figure 8.
Making Examination Easier?
In the great majority of cases, significant differences exist between the visual performance of genuine and counterfeit DOVIDs. Typically, first line detection of counterfeit DOVIDs is based on the absence of distinct visual effects and this allows easy and quick discrimination between valid and fake, as long as the inspector knows what visual evidence must be looked for and how to bring it about.
However, this visual evidence is not standardized; it varies between different DOVIDs and often changes when a new generation DOVID is introduced on a valuable document or product. Additionally, DOVIDs do not provide an explicit clue about how to perform the inspection and what to expect. This complicates the task of the inspector, so could this be simplified? Would it be possible, for example, to specify what visual security evidence should be incorporated in DOVIDs as a standard, to allow easy and secure first line inspection without requiring inspectors to have lots of information in the head (HN November 2004).
Secure banknotes already satisfy this requirement; they have watermarks (often including an electrotype watermark), see-through register, tactile intaglio, optically variable ink, embedded threads and maybe a transparent window in the future. Standard first line security elements in DOVIDs could for instance be blazed grating graphics, zero order graphics, true colour 3D holograms and animations based on both varying grating orientation and frequency, while tilting might be standardized about the horizontal axis. Is this something for the ISO to examine in its new work on authentication solutions and the proposals for hologram standards from Japan?