A Novel Image Watermarking Robust Against Geometric Attack

With the development of the digital media and internet, a new technic named Digital Watermark emerges. It protects the copyright of the digital media, but along with it is the attacks towards the watermarking. Geometric attack is a frequently used technic to make the watermarking unavailable. The attack destroys the symmetry of the watermark system, make the watermark undetectable to legal users. There are several algorithms robust against the Geometric attack. In this thesis, a new scheme is introduced to prevent the geometric attack. The algorithm is robust against geometric attack and has low computing complexity. The main idea of the algorithm is to implement a normalization process before embedding and extracting the watermark. How to get the normalization process is the major work of the paper, CDMA is used in the watermarking process.This dissertation is divided into 5 chapters. The first chapter gives a preview of the watermarking technic, including the development of the technic and the main problems of the technic;the second chapter concludes a mathematic model of image and geometric attack;the normalization precess is derived in the third chapter which is the major chapter of this thesis;in the fourth chapter, the watermarking algorithm based on CDMA is introduced;in chapter 5, we demonstrates the experimental results of the algorithm, finally a conclusion is made to summarized the major point of the dissertation.