An Industrial Watermarking Process for Plastic Card Supports

This paper investigates a robust method to watermark and decode images such as identity pictures printed on plastic card supports that have a special interest in industrial areas requiring secure authentication. The watermark is embedded in two different secret middle frequency bands of the DFT (discrete Fourier transform) and its imperceptibility enhanced via a psychological mask incorporated in the spatial domain. Printing and scanning processes are well controlled in smart card area so than image synchronization is reduced to retrieve small translations and rotation in the spatial domain. This process is therefore simple, efficient and fast. The method interest is demonstrated with several watermarked images printed via common industrial printers and decoded by our home-made industrial reader prototype. Pictures were degraded via the print/scan process and by the "wear and soil test" that simulates the card usage along its lifetime. The correlation is very often above 50% when pictures are decoded with the right keys. It goes down on average to 10% if a wrong key is used as it is the case of an impostor. The process is very reliable: by setting an authenticity threshold to 20%, the probability of false alarm is less than 10^-7.