Robust digital image watermarking using interest points and DFT domain

In this paper we present a robust watermarking method, in which the watermark is embedded into the magnitude of the middle frequencies of the Discrete Fourier Transform (DFT). To allow the correct watermark detection, even if the image has been distorted, the Speeded Up Robust Feature (SURF) is used. During the embedding process the SURF points are estimated and stored in advance to be used during the detection process. In the detection process, the SURF points of the distorted image are estimated, which are used together with the stored ones to compute the affine-transformation parameters. Using these parameters the geometric distortion is corrected before applying the cross-correlation operation used for watermark detection. The quality of the watermarked image is measured using the Peak Signal to Noise Ratio (PSNR) and Structural Similarity Index (SSIM). Experimental results show that the proposed method provides robustness against several geometric distortion and signal processing operations.