Digital Watermarking Method against Rotation Attack Based on Angle Measurement

Abstract

Digital image watermarking algorithm based on contourlet transform and discrete cosine transform (DCT) is proposed in this paper. The original carrier image is decomposed with contourlet transform. The low pass component is divided into sub blocks. The watermark bits are embedded by the quantization of direct current (DC) coefficients of these sub blocks. In order to against rotation attack, the radon transform is used to project the image onto projection space to convert the rotation of the original image to a translation of the projection and then the bi-spectrum analysis approach is applied to estimate the rotate angle of the test image. The detection process is robust to rotation attack by virtue of this rotation correction method.