The Design And Research Of Print-scan Resistant Watermarking Algorithm

With the rapid development of Internet and the widespread use of multimedia digital works, the easy-to-spread distribution and high-quality reproduction and other special features of digital works, making access to high-quality copies of digital works becomes increasing easy. The technology of Digital watermarking aiming at the protection of digital work is a powerful mean of digital right protection, also gets consistently challenge. Print-scan resistant digital watermarking algorithm, used in the environment of print and scan, will be able to solve the issue of copyright protection in the printed works.In this paper, the main target is that the digital images as the original works in the experience of printing process, how to protect the copyright of printed works. Design the print-scan resistant digital watermarking algorithm, embedding watermark before printing digital works, by scanning the printed works to extract the watermark information, so as to realize the rights protection of digital works in the printing process.After describing the basic knowledge of digital watermarking, the paper shows its theoretical significance and practical value. After analyzing the digital image in the printing and scanning process through the main attack of non-linear distortion and geometric distortion, gives the idea by modifying the invariant mathematical feature to achieve the embedding of watermark as the guiding ideology.The paper finds that the sign of the DCT coefficiences of image block is invariant by analyzing the change about the block DCT coefficiences before and after print-scan. Based on this, the paper proposes a double watermarking algorithm based on DCT domain that the coexistence of robust and fragile digital watermarking can be achieved. The robust watermark in the double watermarking algorithm use the invariant feature after print-scan, the relationship between the number of positive and negative coefficients of the same DCT efficiencies class, accomplishes the embedding of watermark by modifying the difference relationship. Experiments demonstrate that the robust watermark can resist the print-scan attack. The fragile watermark in the algorithm enriches the function of the algorithm, making it do well in the Internet environment that needs strong robustness and can determines the location of the digital image tampered with the network transmission.Based on the fact that the unchangeable semantic information after print-scan, the digital presentation of the feature extracted from the low-frequency part of the image's DWT domain, can reduce the effect of the geometrical attack during print-scan process. Accordding to this invariant feature, the paper proposes a digital watermarking scheme that based on image feature. It calculates the low-frequency wavelet coefficients of image, divides it by block and clusters, and according to the difference between the adjacent blocks, gets the polarity table of the image. After scrambling the watermark image to be embedded, combine the polarity table and scrambled watermark to get a key image by using XOR operator, accomplishing the embedded process. The security of the scheme is depended on the scrambling parameters and the key image, etc. Experiment result shows that, when certifying some amount of the bits embedded, the watermark can be extracted accurately, and better than other similar scheme, do implement the copyright protection of printed work.Then, the paper gives the solution idea of achieving the optimum performance among robustness, imperceptibility and capacity of digital watermarking algorithms. When meeting certain required conditions about perceptibility and watermark capacity, digital watermark can reach stronger robustness.Finally, after concluding the main solved problems and achievement, summaries the remained problem in the research of print-scan resistant digital watermarking, and prospects the direction for future research and application.