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Digital watermarking methods of still images using the wavelet transform

Digital watermarking methods of still images can be placed under two categories based on whether they cast the watermark in the spatial domain or in the transform domain. It was found that the transform domain watermarking schemes are typically much more robust to image manipulation as compared to the spatial domain schemes. In this paper, we will present a watermarking method based on the wavelet transform which does not require the original image for watermark detection. In our method, the original image is decomposed using multi- stage discrete wavelet transform. The watermark, generated by pseudo-random sequence, is added to all high-frequency coefficients that are above a given threshold. The watermarked image is finally obtained by using the inverse discrete wavelet transform. For watermark detection, we calculate the correlation between the wavelet coefficients of a possibly corrupted watermarked image and the watermark. By comparing the correlation with a predefined threshold, the embedded watermark can be detected. Experimental results are given to illustrate the robustness against smoothing, cropping, and JPEG compression.