A novel affine attack robust blind watermarking algorithm

In this paper, we propose a novel content-based blind watermarking algorithm which is robust to arbitrary affine transformation attacks. Although watermarking technology has improved remarkably nowadays, algorithm that resistant to geometric transformation attacks remains to be a challenge to the researchers. A small distortion of the watermarked image may lead the failure of many existing watermark detecting and extracting algorithms because of the destruction of synchronization. We present a synchronization method based on the barycentric coordinate representation of the host image. We first segment the host image according to the pixel values, then calculate the weighted center (of mass) of each part, and then select three of these centers to establish a barycentric coordinate system. The host image is represented using this barycentric coordinate system. A squared area is chosen and is decomposed using 3-level discrete biorthogonal wavelet transform. The watermark is embedded in the middle bands of the wavelet decomposition of the represented host image using a CDMA based algorithm. The watermarked image is obtained by inverse wavelet transform and inverse barycentric coordinate transform. In the watermark extraction phase, the same segmentation should be done on the received image, and the received image should be represented using the barycentric coordinate system, and a corresponding squared area is chosen and decomposed using the same biorthogonal wavelet transform as used in the watermark embedding phase, and then the watermark is extracted from the middle bands using the CDMA based algorithm. The proposed algorithm is absolutely blind. Multi-bit information can be embedded in the host image. Experimental results show that the proposed algorithm is robust to arbitrary affine transformation attacks and many other attacks.