A secure and robust digital image watermarking scheme using repetition codes for copyright protection

Abstract

Digital Image Watermarking is used to hide the copyrighted information as a watermark inside a Digital image, to identify the ownership. In this paper to ensure the security watermark is first encrypted by standard A5/1 algorithm. The encrypted watermark is encoded by repetition code to provide robustness against salt and pepper noise and embedded inside the cover image by modifying the least significant bit of cover image pixels. The perceptual quality of watermarked image remains almost unchanged. Normalized Correlation (NC) and Bit Error Rate (BER) are computed for performance evaluation. It is seen that for noise densities considered BER is largest and NC is least when encrypted watermark pixels are not encoded. Using (n, 1) repetition code for n=3, 5, 7, 9, 11, 13 BER of extracted watermark progressively decreases and NC increases for various noise densities. Further, with (13, 1) repetition code watermark can be extracted even with noise density up to 0.6, with reasonably good visual quality.