Semi-fragile watermarking algorithm based on bi-watermarking technology

A semi-fragile watermarking algorithm using bi-watermark is proposed in this paper. When embedding watermark, the original image was decomposed by 3-level discrete wavelet first, and then edge information of the third approximation coefficient was extracted using canny operator. It was embedded into the third vertical detail coefficient by QR decomposition and replacement getting fragile watermark. Principal component of the third approximation coefficient was got by PCA and embedded into the third horizontal detail coefficient as robust watermark. In the end, the approximation coefficient, changed detail coefficients were constructed to obtain image having watermarking. When authenticating image, the observed image was decomposed by 3-level discrete wavelet first. Image could be authenticated correctly and attacked parts could be localized through comparing the original watermarks and extracted watermarks. Experimental results show the efficiency and feasibility of this method.