The Study Of Fragile Digital Image Watermarking With Restoration Capability

With the rapid development of Computer and Network technology, the problem of information security has become increasingly important. The encryption methods can give the solution for this problem to some extent. However, this can not radically prevent the pirates and tampers. After the multimedia data is decrypted, it is in the clear and no longer protected. While digital watermarking which is one of the research focuses in the academic world presents a candidate key to the questions.The watermark with a special function is embedded into the multimedia information to protect the copyright of the original author and authenticate the integrity and authenticity of the multimedia information. The watermark technique has become one focus of researcher.The attention of dissertation is focused on constructing the image authentication system based on the watermarking, and the main work is listed as follows: First, an introduction of the characteristics, principles, classifications and current research situation of watermarking are given. The basic framework of the digital watermarking system is summarily proposed. And the present familiar digital watermarking algorithms are introduced briefly. Second, the theories of the DWT, cryptology, the chaotic encrypt and the image scrambling techniques are proposed. The application of the DWT theories is extensively studied. How to increase the security of the watermarking system by the knowledge of encryption is analyzed. The methods to encrypt the watermark by the chaotic sequences are introduced. The application and means of shuffling techniques within watermarking are extensively discussed. Third, an auto-restorable fragile watermarking algorithm for image content authentication is proposed. The main idea of this algorithm is described as follows: Important DWT coefficients are chosen to be coded with the SPIHT algorithm for generating watermarking. Then the improved security watermark scrambled by Arnold transformation is embedded into the lower bits of the image data. Finally, chain structure is used to detect watermarking and identify the changed positions .And the altered data in an image is restored by SPIHT decoding. The experimental results demonstrate that the watermarked image not only possesses good perceptual transparence but also can locate and restore the tampered content.At last, work of dissertation is summarized, and the further research direction is discussed. The digital watermarking algorithm given by the dissertation has been applied on the VC++6.0 platform. The experiment results are satisfactory.