In this paper, we present a hybrid digital watermarking scheme for copyright protection purposes. Our scheme is based on a multi-resolution wavelet analysis. For a robust watermarking, the watermark must be embedded in the lowest possible spatial frequencies. However, a problem with this is that very low frequencies modifications are difficult to implement without a perceptual distortion in the original image during the watermarking process. We found that wavelet transform is a good tradeoff for this problem. Wavelet transform is known for its good localization in time and frequency domains, a feature that allows for embedding of the watermark in any particular frequency-band and/or orientation. By selecting an appropriate frequency band at which we fuse the watermark, robustness can be achieved for both applications of copyright-protection and tamper-proofing. To evaluate our algorithm, we demonstrate the effects of various image distortions and attack operators such as mean filtering and JPEG compression. Our results indicate that the proposed algorithm is more robust when compared to other algorithms in the same category. In addition, our watermarked images did not show any visible artifacts, and the original image is not required to extract the watermark.
Mohammed A. Al-Mohimeed,
"Wavelet-based digital watermarking", Proc. SPIE 4314, Security and Watermarking of Multimedia Contents III, (1 August 2001); doi: 10.1117/12.435425; https://doi.org/10.1117/12.435425