TABLE OF CONTENTS The counterfeiting of banknotes and other financial transaction documents as well as visas, passports, ID cards, other official Government security papers and the counterfeiting of software, pharmaceuticals and brand name products is now becoming one of the world's fastest growing areas of criminal activity. With the advent of colour photocopiers and digital scanning devices the traditional security printer's skill and craftsmanship is no longer sufficient to protect the integrity of high value documents (Pagan 1990). According to the International Chamber of Commerce Counterfeiting Intelligence Bureau over 5% of world trade consists of counterfeit product. The cost of this illegal activity amounts to over US$350 billion annually and is growing. To counteract this rapidly evolving threat security printers and central bank issuing authorities have turned to new technology in the form of the diffractive Optically Variable Device (OVD) (Renesse 1994). Mass produced by embossing into hot stamping foil, these diffractive surface relief microstructures have proven to be a highly effective solution to the counterfeiting problem. The key security feature underpinning all optically variable devices is, as the name implies, the variability of the image with changing angle of view or changing angle of illumination by a light source. This image variability can even take the form of a switch between one artwork pattern to a totally different piece of artwork; from the image of a face to the number 50, for example. Because of this image change effect these devices cannot be copied by the usual photographic, computer scanning...
