A Robust Image Zero-Watermarking Algorithm Based on DWT and PCA

Zero-watermarking which doesn't modify the original image but constructs zero watermarks from it, is a useful technique for resolving the contradiction between robustness and invisibility. In this paper, a robust image zero-watermarking algorithm that based on Discrete Wavelet Transformation (DWT) and Principal Component Analysis (PCA) is proposed. In the proposed algorithm, the original image is first transformed with DWT, and its LL band is divided into nonoverlapping image blocks with each image block transformed into a vector, and then it performs a PCA on the set of vectors. Finally, it constructs the zero-watermark sequence by judging the positive and negative polarity of the coefficient which has the maximal absolute value in each analyzed vector. The robustness of the proposed algorithm to given image processes is analyzed, and the results show that the proposed algorithm is very robust to conventional signal processing, such as noise, filtering, JPEG compression, and cropping etc.