Affine Transformation Resistant Watermarking Based on Image Normalization
Geometric attacks are among the most challenging problems in present day watermarking. Such attacks are very simple to implement yet they can defeat most of the existing watermarking algorithms without causing serious perceptual image distortion. In this paper we propose a new public watermarking algorithm, which is robust to such attacks. This algorithm uses a normalized with respect to affine transformation representation of the image based on the image moments. Then, a CDMA scheme is used to embed a multi-bit watermark in the discrete cosine transform domain of the normalized image. Numerical experiments are shown where the properties of the proposed algorithm are tested. These numerical experiments show that the proposed algorithm is very robust to wide range of geometric attacks.
Ping Dong, and Nikolas P. Galatsanos
Department of Electrical Engineering, Illinois Institute of Technology
1. INTRODUCTION Although lot of progress has been made in watermarking research and application recently, geometric resistant watermarking remains to be one of the most difficult outstanding areas. A small distortion, such as rotation, scaling, translation, shearing, random bending or change of aspect ratio, can defeat most of the existing watermarking schemes claimed robust. Such distortion can destroy the synchronization, which is required by the above mentioned watermarking techniques. This problem is even more pronounced when multi-bit public watermarking is needed in practical application, which means the original unwatermarked image is unavailable for watermark extractor and the application need to embed multi-bit information, such as copyright ownership or license numbers. To our knowledge, J' Ruanaidh and T. Pun are the first to suggest a Fourier-Mellin transform based watermarking scheme to handle geometric attacks, such as rotation, scaling and translation (RST). The algorithm seems workable theoretically, but proved to be difficult in implementation. C. Y. Lin and M. Wu, etc] proposed an improvement to the implementation difficulty by embedding the watermark into an 1-dimensional signal obtained by projecting the Fourier-Mellin transformed image onto log-radius axis. Such algorithm can embed only one bit information, i.e. presence or absence of the watermark, and the implementation is still a headache and far from practical application. Pereira and Pun proposed an approach to embed a template into the DFT domain besides the intended watermark. Parameters of affine geometric attacks are estimated through the detection of template. Then affine distortions are recovered using the estimated parameters and detection of watermark is performed from the recovered image. To such an algorithm, a correct positive detection requires that both the payload-carrying marks and the synchronization pattern be successfully embedded and detected. A second problem arises when many images watermarked with this method share a common template. This can ease the collusion detection of the template and pose security threats to the template itself . Moment based image normalization has been used in computer vision for pattern recognition for a long time. Its use in watermarking was first reported in . The scheme handles flipping, scaling and rotation attacks, and it is only used to embed 1-bit information. In this paper, we present a blind normalization algorithm (BNA) based multi-bit public watermarking scheme to handle general affine geometric attacks. Fig.1 illustrates the normalization based watermarking system. The main differences between our scheme and the one used in is that, first, general affine distortion is addressed instead of specific geometric attack, and second, a CDMA based multi-bit watermarking system is proposed while handle 1-bit watermarking.