Detection of Periodic Pilot Signal in Image Watermarking

A watermarking method that has robustness against geometric and non-geometric attacks is desired. Conventional methods extract watermarks regardless of the type of attacks. For example, error correction codes have been used to correct errors in watermarks, but these methods have limitations. If we could identify the type and strength of attacks, we might be able to achieve fewer errors. To detect the attacks, a method that embeds a template in the discrete Fourier transform (DFT) domain has been proposed. This method has issues in that template matching takes a very long time and it does not support clipping since it uses the DFT domain. Therefore, we propose a method to estimate the magnification ratio by embedding a pilot signal in a non-transformed domain. A watermark and the pilot signal are embedded in the Y and U components, respectively. In this study, a grid pattern was used as the pilot signal. The magnification ratio was estimated by extracting the periodicity of the grid pattern. As a result, for uncompressed images, the estimations were almost accurate. For compressed images, the results were mostly accurate as long as the Q factors were above 60.