A novel robust digital image watermarking algorithm based on two-level DCT

In this paper, we propose a novel blind digital image watermarking algorithm which is resilient to many kinds of image processing attacks and geometric distortions. To embed the watermark, we first map the original watermark to another spread one aiming to fit for the image size and then embed it into the image two-level DCT coefficients we selected using a specified rule. We extract the watermark using two-level DCT accordingly with the help of the correlation scheme. Comparing with other achievements, our proposed schemes, including spread spectrum watermark generation, block-number-fixed image segmentation, two-level DCT and the feature vector extraction rule, play an important role in improving the watermark robustness. Experimental results demonstrate that our method can not only resist common image processing attacks, but also geometric distortions, such as scaling, aspect ratio changing, flip, rotation, and some kinds of combined transforms.