Study Of Digital Watermarking Algorithm On Color Images To Resist Hard-copy Attack

Along with the need of copyright protection and certification for printed paperpublications, in this thesis color image watermarking algorithms and techniques to resisthard-copy attack in practical application have been studied.This thesis firstly gives an analysis of distortions an image undergoes when it beingprinted and scanned, and of some challenges to image watermarking caused by thesedistortions. Based on the analysis, a DCT coefficients statistics-based print-scanresistant watermarking algorithm is advanced. Compared to the original one, the newalgorithm is proved having better robustness and invisibility which introduces the HVSmasking model as the adaptive watermarking strength factor and improves the datacapacity significantly.A watermarking algorithm based on image subsampling is introduced then, whichembed the watermarks through a way of changing the luminance relationship of blockpairs in subimages. This method adjust the embed strength according to the luminancecharacteristic of block pairs. Some promotions and experiments are also taken toimprove the performance. This method contributes a new idea to the research ofprint-scan resilient watermarking schemes.