A hybrid fusion technique for watermarking digital images

A hybrid fusion technique (HFT) that offers improved imperceptibility, better robustness to attacks and superior quality in terms of watermark image recovery than is realisable using the traditional Discrete Wavelet Transform (DWT), Discrete Cosine Transform (DCT) digital watermarking techniques or methods that utilise their direct combination is presented in this work. The separate DWT and DCT methods embed the watermark image directly on the wavelet or cosine coefficients of the cover image, while methods that combine both the DWT and DCT are certain to directly embed the watermark on some parts of the cover image twice. Unlike all these methods, our proposed HFT technique spreads the watermark in the transform (wavelet and cosine) domains separately and then the watermarked images from the two images emanating from the two domains are fused together to generate the final watermarked image - producing a hybrid. Such hybridisation allows us to exploit the individual benefits derivable from the separate use of the DWT and DCT methods. Experimental evaluations show that combining the two transforms in this manner offers improved performance in terms of imperceptibility, robustness to jpeg and other kinds of attack on the published (watermarked) image and quality of recovered watermark image than is obtainable using the methods that are based solely on the DWT or DCT techniques or their direct combination. The proposed HFT technique guarantees additional protection for digital images from illicit copying and unauthorised tampering.