Digital Watermarking Algorithm Based On DCT Domain And Its Application In Copyright Protection

With the rapid development of information technology and Internet, the storage and transmission of multimedia information become more and more fast and convenient, which provides great convenience to people’s lives while also brings a lot of difficulties for copyright protection. People can easily download digital products from Internet and falsify them, which may cause copyright disputes. Thus digital watermarking technology is proposed to solve those problems. Recently, the common digital watermarking algorithms include LSB algorithm and DCT domain algorithm, the first one focuses on the invisibility and the second one focuses on the robustness.Pointing at two formats:image and audio, two kinds of improved DCT domain algorithms are proposed based on the Cox algorithm. When dealing with the image, the watermark is firstly encrypted with Arnold transform, then according to the encrypted watermark binary image, the relevant information can be embed into the DCT frequency coefficients of the vector. When dealing with the audio, the watermark is firstly encrypted with a random key, and then the wavelet transform is involved since the sensitivity of the audio signal is taken into consideration. Finally, we can compare the encrypted watermarking information to the transformed carrier signal to derive a key and embed it into intermediate frequency coefficients of carrier audio. The simulation result shows that both of the two algorithms have good invisibility. There is no difference between the carrier with a watermark and the original one.On the basis of the two improved algorithms, we designed and implemented a copyright protection system for the image and audio. The system is divided into three modules:data source obtaining module, multi-format conversion module and watermark adding module. The multi-format conversion module can solve the problems that the existing systems only support independent format and have very narrow range of applications. Before adding a watermark, the function of image format conversion and audio format conversion is involved, thus we can add a watermark to the image and audio with all popular formats. Simulated attack experiments show the multimedia system with watermark is robust and can withstand most attacks.This thesis includes33figures,7tables and56references.