DCT-OFDM based watermarking scheme robust against clipping attack

Robustness against various attacks involving lossy compression like JPEG and clipping is inevitable requirements for digital watermarking schemes. In this paper, we propose a watermarking scheme robust against the JPEG compression and a clipping attack using the DCT-OFDM based watermarking method. Robustness against the JPEG compression can be achieved by embedding watermark information into the low-frequency components. We employ the QIM method to the DCT-OFDM modulated signal. By embedding a synchronization signal, we attempt to recover the synchronization loss from a clipped image. In a preliminary experiment, we can detect the embedded synchronization signal around a correct synchronization point because the synchronization signal is mainly embedded into the low-frequency components in a spread form. Then, we determine the center among the detected points as the correct synchronization point. We evaluate the performance of our method by computer simulation. It is revealed that our method satisfies the evaluation criteria determined by IHC Committee, while maintaining high image quality.