foster + freeman

Concealed information on a document may be revealed by examining the document under visible or near infrared light. A number of effects may be exploited:-

• If the masking ink is transparent to near infra red light and the underlying ink is opaque, the underlying information will be revealed using either incident or transmitted infra red light and a suitable infrared high pass filter.
• If the masking ink is slightly transparent to visible light and the underlying ink is photoluminescent, the masked information may be revealed by illuminating the document with intense visible light, some of which will penetrate the masking ink to induce the underlying ink to fluoresce. Although very weak, the fluorescence signal may be integrated to produce a strong legible image.
• If the masking ink is fluorescent and the underlying ink absorbs the fluorescence the underlying information may be revealed by examining the document under intense visible light.

Above Image: Infrared fluorescence emitted by the concealed ink is sufficient to penetrate the masking ink when illuminated by intense visible light. The weak emission is integrated until visible

This is normally a straightforward process of examining a document with transmitted light but examinations may be made easier with a variety of additional techniques.

For example, it is possible to eliminate printing or handwriting on the surface of the document that is masking the watermark by examining the document in the infra red rather than the visible. Alternative display modes, in which original and counterfeit images are superimposed or displayed side by side, also make comparisons easier.

Above Image:A Portugese visa under longwave UV showing fluorescent features

Special features which are invisible to the eye but which fluoresce brightly under ultraviolet light are often printed on or incorporated into security documents to deter counterfeiting. The VSC 6000 provides a range of UV lamps to examine these features. In addition to visual examination, fluorescence spectra and colour co-ordinate measurements can be made on samples as small as 62 microns square.

• long wave incident UV, 365nm peak wavelength
• medium wave incident UV, 312nm peak wavelength
• short wave incident UV, 254nm peak wavelength
• long wave transmitted UV, 365nm peak wavelength

Above Image:Dutch passport under normal lighting(top)- Dutch passport showing retro-reflective features under co-axial lighting (bottom)

Retro-reflective features are elaborate graphic designs that are incorporated into security documents to prevent counterfeiting. They are printed with special coatings that render them invisible under normal light and can only be seen with illumination that is precisely coaxial to the angle of view. The VSC 6000 provides the appropriate lighting and imaging systems to enable these features to be examined and printed.

Above Image:A Chinese banknote showing the security features printed with anti-Stokes inks and illuminated with infrared light.

The VSC 6000 provides infrared illumination above 800nm that is free of visible light, making it possible to examine security features on documents and identity cards printed with anti-Stokes security inks. These inks have been designed to fluoresce in the visible region of the spectrum when illuminated with infrared light.

Above Image:An OVD on a 500 euro banknote (above) viewed with angled illumination and a series of different OVD images on a 5 euro banknote(top)viewed using sequential, multi-angled illumination.

OVDs on security documents commonly exhibit different images when illuminated at different angles. The VSC 6000 is fitted with 14 white LEDs in horizontal and vertical arrays to provide sequential illumination at varying angles of incidence. The multiple images comprising the OVD may be stored and displayed without tilting the document.

Inks on a document that are identical in colour but have different chemical compositions may provide evidence of an alteration when examined in the near infrared region of the spectrum. Although undetectable with the naked eye, a near infrared image is easily converted into visible one, using an infrared sensitive video imaging system such as the VSC 6000. Two techniques may be used.

The first is to look for differences in the near infrared light reflected or transmitted by the two inks. The document is illuminated with either incident or transmitted broadband infrared illumination and examined through a range of long wave pass filters with increasing thresholds between 650nm and 1000nm. Any difference in the spectrum of the transmitted or reflected light will become evident under at least one of the filters.

The second is to look for differences in the photoluminescence or fluorescence emitted by inks and, again, this is normally observed in the red to near infrared region of the spectrum. This fluorescence may be generated by illumination with intense visible light that has been filtered free of near infrared. As before, an examination of the document is conducted through a range of long wave pass filters with increasing thresholds between 650nm and 1000nm. Any difference in the spectrum of the fluorescence will become evident under at least one of the filters.

The VSC 6000 provides the examiner with the sensitive infrared imaging system and the light sources and filter sets to perform both types of examination. Image integration is also provided to enhance the fluorescent images which are often of very low intensity.

The VSC 6000 features orthoganol oblique lighting, illumination from two light sources at different angles, that provide the examiner with a clearer image of indented writing or embossed stamps.

However, not all such examinations are straightforward, as the presence of printing or handwriting on the document may interfere with the image and hinder examination. When the ink causing interference is transparent to near infrared light, it can be eliminated by conducting the examination at this wavelength. After the VSC 6000 converts the infrared image to a visible one the ink will appear to vanish while the infrared shadow remains. The VSC 6000 enables such examinations to be made at wavelengths in the near infra red up to 1000nm.

Although the shadow casting technique is useful for examining deep indentations and embossing, shallow indentations or those not visible at all, are more effectively examined using an electrostatic imaging technique.

See details of the company's product ESDA².

Graphic designs and logos on original documents and product labels are often inaccurately reproduced on counterfeits. These inaccuracies are easier to detect by examining original and counterfeit either side-by-side or by superimposition at high magnification.

Matching tear profiles between fragments of paper is another example where the VSC 6000 can be effective. If the image of one fragment is stored and displayed as a virtual object, it can be superimposed on the real image of a second fragment without the fragments coming into contact. This prevents distortion of the edges as one fragment is moved relative to the other.

A range of comparative display modes are available on the VSC 6000 as standard.

One of the simplest ways to detect a counterfeit document is by visual comparison with a genuine one. With the VSC 6000's wide display screen, high resolution and zoom magnification up to x140, discrepancies in fine detail are easier to detect when documents are displayed side by side. Both images can be annotated with text and symbols and both have notepads attached on which observations can be jotted down.

Above Image:The colour co ordinates of six blue inks displayed on a chromaticity diagram

Colour co-ordinates are a useful way of defining colours and provide a convenient way of recording and comparing colours objectively. The VSC 6000 enables colour to be measured in both the standard 1931 and 1960 CIE colour co-ordinate systems.

Colour co-ordinates can be displayed on chromaticity diagrams which provide effective graphic evidence of colour differences, especially when the colours of many samples need to be compared. Colours, which differ in intensity only, have co-ordinates that lie on a common colour radial. Colours with true spectral differences lie on different colour radials.

Both colour coordinates and chromaticity diagrams may be stored in the VSC 6000's casework filing system for future reference.

The VSC 6000 enables four types of spectra between 400 and 1000nm to be measured - absorption, reflectance, transmittance and fluorescence. These may be used as further aids in the identification of counterfeit documents.

Absorption and reflectance spectra are measured with reference to a standard white tile to provide absolute measurement. Transmission spectra are measured with a dual beam system for normalisation. Fluorescence spectra are measured without a reference signal, and are therefore subject to the spectral characteristics of the camera and lighting. Weak fluorescence may be integrated by up to 10 seconds before analysis, considerably enhancing the sensitivity of the spectrometer in this application.

The VSC 6000 also provides a number of facilities for processing spectra; normalisation, to eliminate the effects of a background to allow spectra on different substrates to be compared; subtraction, to highlight differences in spectra and differentiation to identify wavelengths of greatest change.

Spectra may be retained in document records under the VSC 6000's general casework management system.

With high resolution imaging the VSC 6000 enables the operator to display up to 60 stored images on a single screen to provide a quick method of retrieving a stored image.

Measuring specific features of a document often provides valuable evidence of a counterfeit. The VSC 6000 enables the radius, length, angle and area of a feature to be measured using an on screen cursor. Calibration provides absolute measurements and the instruments high magnification range allows the smallest features to be examined.

'Quick Check' is a new feature of the VSC 6000 that enables an operator to make a sequence of document examinations under a variety of fixed, pre-programmed instrument settings. The facility is designed to standardise the repetitive examination of large numbers of similar documents such as passports, ID cards or cheques, suspected of being altered or counterfeited.

Once programmed under Quick Check, the VSC 6000 automatically adopts the mode of illumination, lamp filter, imaging filter and lens magnification appropriate to the examination task selected, minimising operator performance errors.

Each stage of a multi-task examination sequence can be initiated either manually or automatically. Under automatic operation, each instrument setting is maintained for a predetermined period of time to allow the operator to carry out the examination before moving on to the next stage. Reports may be filed for future appraisal by a supervisor or expert examiner.

The technique can save time, ensure consistency in procedure and is particularly suitable for use by technician operatives.

The VSC 6000 features an optical character reader that allows the operator to examine the ICAO coded data in the machine readable zone of passports and ID cards.

Once the operator has selected the appropriate country from the menu, the OCR deciphers, checks and displays the information held in the machine readable zone of the document under the instrument.

Personal information invisibly embedded in photographs has become a valuable technique for protecting passports and ID cards against forgery. To visualise the information the operator simply selects a country to automatically apply the appropriate decoder. The system covers most systems currently in use and new ones can be added by the operator as they arise.

The VSC 6000 enables the operator to create comprehensive casework files, in which images, spectra, chromaticity charts, notes and observations may be stored. Images have associated instrument settings, i.e. type of illumination used, camera filter, integration time and magnification, which enable the operator to recreate identical conditions when making subsequent document examinations.

Images may be annotated with text and symbols and each is provided with an on-screen working notepad for the operator's convenience while conducting an examination. All stored images, charts and spectra and associated notepads may be interfaced with Microsoft Word for report writing.

Image search facilities allow the operator to retrieve stored images by name, file type (i.e. Tiff, BITMAP, JPEG, etc), keyword with wild card and by approximate date of entry (between two dates). A pull-out gallery of all recently stored images provides a short-cut to image retrieval and to browse all images stored in a casework folder, a thumbnail gallery will display 60 images at a time.