Two digital image watermarking techniques that have higher level of security compared to most of the existing algorithms have been proposed. The proposed digital watermarking scheme uses the properties of discrete cosine transform (DCT) and discrete wavelet transforms (DWT) to achieve almost zero visible distortion in the watermarked images. These techniques use a unique method for spreading, embedding and extracting the watermark. Embedding using a linear relation between the transform coefficients of the watermark and a security matrix has been proposed with satisfactory results. It has been shown that instead of adding the watermark to the source image, as is normally done, multiplying the watermark with the transformed source could be a preferred technique, as it would retain the original bit rate to a large extent. The watermarked images were tested subject to image cropping.
Dr. Shikha Tripathi, Jain, R. C., and Gayatri, V., “Novel DCT and DWT based watermarking techniques for digital images”, in Pattern Recognition, 2006. ICPR 2006. 18th International Conference on, 2006.