| Summary: | 碩士 === 國立清華大學 === 資訊系統與應用研究所 === 98 === In the rapidly development of the internet, the image content will be more easily be copied or tampered while delivering trough the net. The paper chooses the Semi-fragile watermarking technique. Semi-fragile watermarking can resist legal manipulations such as JPEG compression, and detect the tampered image. Therefore, it can be used to authenticate the image and detect if the image is tampered. For the blind scheme, we propose the Modulate mechanism to embed the watermark pattern.
After embedding the watermark into the image, we hope to maintain the high quality and correctly detect the changed signal of the image even if it under the normal image processing. To match this goal, we choose Game Theory to analyze it. In Game Theory, two features of the Semi-fragile watermarking, Authentication and Tamper Detection are considered as two players who compete in the game. And the quality of the image is considered as the resource that two players have to compete. By the analysis of the Cournot model, it can find the best solution to control the image quality.
We compare the proposed method and the average resource allocation method to find that our method can work even in JPEG compression 70%. Finally, the results are applied to design an efficient Discrete Cosine Transform (DCT) semi-fragile watermarking system which allows detecting local forgery signals in spite of JPEG compression.
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