  Digital media can be distributed via Internet easily, so, media owners are
eagerly seeking methods to protect their rights. A typical solution is digital
watermarking for copyright protection. In this paper, we propose a novel
contourlet domain image watermarking scheme for copyright protection. In the
embedding phase, we insert the watermark into the image using an additive
contourlet domain spread spectrum approach. In the detection phase, we design a
detector using likelihood ratio test (LRT). Since the performance of the LRT
detector is completely dependent on the accuracy of the employed statistical
model, we first study the statistical properties of the contourlet
coefficients. This study demonstrates the heteroscedasticity and heavy-tailed
marginal distribution of these coefficients. Therefore, we propose using two
dimensional generalized autoregressive conditional heteroscedasticity
(2D-GARCH) model that is compatible with the contourlet coefficients. Motivated
by the modeling results, we design a new watermark detector based on 2D-GARCH
model. Also, we analyze its performance by computing the receiver operating
characteristics. Experimental results confirm the high efficiency of the
proposed detector. Since a watermark detector for copyright protection should
be robust against attacks, we examine the robustness of the proposed detector
under different kinds of attacks.
