Research On Multipurpose Watermarking Algorithms For Image Authentication And Copyright Protection

Nowadays, technology develops rapidly; computers and Internet have become an indispensable element in people's lives. More and more products exhibit to people in digital form following by the increasingly flinty problems of copyright bother. Encryption techniques can be used to protect digital data. However, after the decryption of the data, the data is in the clear and no longer protected. Digital watermarking is another effective solution that is regarded as the last line of defense. Chaotic encryption technique can enhance security of digital watermarking.Based on chaotic encryption, multipurpose watermarking algorithms for image authentication and copyright protection are studied in this dissertation. The main research contents can be summarized as follows.Firstly, a multipurpose image watermarking algorithm based on chaos and DWT(Discrete Wavelet Transform) is proposed. The original watermark is divided into the robust watermark and the semi-fragile watermark for copyright protection and image authentication. According to different applications, the robust watermark is also divided into two kinds of watermark, one has small capacities and relatively high robustness, the other has large capacities and relatively low robustness. They are embedded to different parts of DWT domain, so is the semi-fragile watermark. The security of the watermarks is enhanced by utilizing general cat map to scramble the robust watermark and using Logistic chaotic system to generate the semi-fragile watermark. Simulation results show that watermarked images have good visual quality, the robust watermark can resist common image processing operations, and the semi-fragile watermark can detect and localize precisely the content tampers.Secondly, a multipurpose image watermarking algorithm based on chaos and mixed frequency domain is proposed. The original image is transformed by DWT to get the low frequency sub-image, and the sub-image is split into sub-blocks. Then, the robust watermark which has been scrambled is embedded to high frequency coefficients of DCT(Discrete Cosine Transform) domain of sub-blocks, and the embedding process is based on the dithered modulation technique. Furthermore, the semi-fragile watermark generated by chaotic system is embedded to the high frequency sub-image of DWT domain, and the odd-even quantization embedding algorithm is used. Lastly, the simulation demonstrates that the algorithm is effective.Finally, this paper concludes by summarizing the research and indicating its future research directions.