Digital Watermarking Algorithm for Print-and-Scan Process Used for Printed Matter Anti-counterfeit

In order to solve the pixel divergence problem brought by print and scan process, propose the algorithm that applying stretching contrast grade to adjust image pixel divergence. The parameter setting of this adjusting method uses peak signal noise ratio as standard of measurement, even though using different printer and scanner, we can also get good adjusting image. Simulation results show that the method can improve the effect of watermark detection or extraction effectively. Based on the character that symbol of parts of image’s DCT coefficient will not change, we propose self-adapting resist print and scan digital watermarking algorithm based on partitioning DCT. This algorithm imbed watermark adaptively, it can improve the capability of imbedded watermark and can also maintenance image quality. Experiment result shows that this algorithm can realize anti-counterfeit of soft-cover certificate using watermark technology.