Digital Watermarking For Print And Scan Process Based On Document Image

With great development of the network technology, the protection of multimedia is more and more important, and the information hiding technology developed. After many years of development, the study of protection for digital image is mature, but what can't ignore is: most important papers like business documents, certificates, confidential documents presented by the way of printed materials. In the past, the algorithms of digital watermarking are designed mainly for the copyright protection of digital media, not for application to print images. The main reason is that printing and scanning maybe affect the digital watermarking, after two times conversion of types from D/A to A/D, most watermark can't be detected or extracted correctly. In this thesis, we summarized the research background, application of digital watermarking and the state of the art, then focus on the watermark which is based on the document image applied to against printing and scanning. The valuable research fruits are as follows.The affects in printing and scanning to image are discussed, we find that the effect of printing and scanning process on special domain is obvious. Since embedding data in halftone images deal with two times conversion of types, it requires very strong robustness, we have to find the stable feature for embed watermark. According to the characteristics of document image, The effect of printing and scanning process on DWT is analyzed, and a watermarking algorithms which suit for document image is designed. Experimental results show that the new algorithms is of very strong robustness, can stand against the printing and scanning attacks, the images with embedded data are of good quality, and the original image is not needed in the recover progress . This algorithm can be used for forgery detection of important document image.Finally, the application of proposed watermarking algorithm in a paper check system is studied. Mainly studied the preprocess technology about our algorithm, including binarization, denoising, undoing rotation and segment. Analyzing the experimental results we find that the preprocess play an important role in watermark detecting, and give the future work.