| Digital watermarking as a new mean to provide copyright protection and authentication of multimedia data has been developing rapidly since 1990's, and becomes an internationally hot topic at present. A digital watermarking technology allows users to imperceptibly embed a specifically signal (the watermark) into multimedia data such as image, text, video and audio by a certain proposed algorithm in order to protect multimedia data and authentication. This paper first reviews some fundamental theories of digital watermarking, then for digital image watermarking, systematically presents two schemes. One scheme is a robust watermarking algorithm based on discrete cosine transformation domain, the other scheme is a robust watermarking algorithm based on discrete wavelet transformation domain. The two algorithms quote a chaotic dynamical system to preprocess the watermark, and combine human visual system to adjust imbedded intensity to better coordinate the contradiction between imperceptible thing and robust one. The experiment result indicates that both schemes have very high peak signal-to-noise ratio, improve watermark's imperceptions; and it is robust to JPEG compression, noise, and cropping. A fragile watermarking based on DWT domain for authentication in digital images also introduced, and creativity present a rule to distinguish the patterns of tamper between mild distortion and severe distortion. Experiment simulation demonstrates the rule can accurately distinguish signal distortion such as compression, noise and severe distortion; and the algorithm is robust to JPEG compression so that it is suitable for multimedia transmitted in network. The digital watermark mentioned here is only for digital image; those for audio and video are not concerned in this thesis.
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