Research On Image Copyright Protection And Authentication Technology Based On Digital Watermarking

With the rapid development of network and multimedia information technology, safety of multimedia information is the biggest problem, so digital watermarking technology has been mentioned. As a new information safety technology, digital watermarking technology embeds invisible extra information in digital media, tracks using process of digital multimedia by detecting the embedded information and realizes the functions of information embedding, storage and copyright protection. Nowadays digital watermarking technology has gradually become a effective method for multimedia copyright protection and integrity authentication.As an important part of multimedia information safety, information safety of digital images is focused in this thesis. At first, the basic theory and technology of digital watermarking, especially the digital image watermarking technology, is introduced. Then to realize the copyright protection and authentication of digital image, several improved algorithms are proposed, which are detailed as follow:1. To enhance the capability against geometric attack of digital images, an improved algorithm based on Harris feature point correction and DCT domain, is proposed. In this algorithm stable Harris feature points are utilized to geometric distortions correction, and watermark embedding in global DCT domain and correlation detection are incorporated to correct severe geometric distortions and to gain high quality watermarked image. In the process of Harris geometric distortions correction, an improved match algorithm based on detection matrix is provided to overcome the disadvantages of enumerative search match algorithm and match process is speeded up greatly.2. For image integrity authentication, an improved DCT domain semi-fragile algorithm is proposed. In this algorithm, the marginal information in DCT domain is used as original watermark, then is encrypted by chaos sequence and is embedded by replacing LSB bits on selected low frequency location in quatitative DCT coefficients. The immunity to noise, especially to severe JPEG compress, is strengthened in certain extent. Intended modification can be detected and located exactly and the conflict between robustness and fragility in semi-fragile watermarking algorithm is eliminated.3. For counteract of image processing attack, an improved DWT domain robust watermark algorithm is proposed. In this algorithm, according to the different robustness of different subband for different attack after multilevel wavelet translation, redundancy watermark is embedded in optimally selected domain. The robustness to noise(salt&pepper, Gauss), filtering(median, average, low-pass, high-pass), brightness adjustment, contrast adjustment, JPEG compress and cutting operation is strengthened.4. Based on the mentioned algorithms above, a multipurpose watermark algorithm for color image is proposed, and copyright protection and authentication function for color image are realized at the same time. In this algorithm, different watermarks are embedded in color component of image, one for image authentication and the other two for copyright protection against geometric attack and image processing attack separately.Finally the author just makes a conclusion of the whole paper and proposes future research directions.