A Novel Zero-watermark Algorithm in Image Subspace Domain

Traditional digital watermarking techniques protect the copyright of the image by embedding the watermarking into the image can lead to distortion, and furthermore, it is difficult to extract watermark from attacked image. This paper brought forward a novel zero-watermarking method, which could protect the copyright of the image without affecting the image quality. The central idea of this method is to subdivide the image block by block, and use K-L transform to decorrelate the image pixel to get the signal subspace and noise subspace of an image. Based on Renyi mapping, a chaotic sequence is generated and the signal subspace is threw into confusion, and then a characteristic watermark is generated by comparing the coefficients of confused signal subspace. The same process was done to draw the characteristic watermark out from the authentication image and the conformability of two watermarks was analyzed for judging the copyright and the ownership of the image. Experimental results demonstrate that this method is invisible and strongly robust against some usual attacks such as JPEG compression, median Filter, clipping and rotation.