Visual Cryptography based Secured and Robust Digital Image Watermarking

Digital ImageWatermarking is a process of embedding a copy righted information inside the digital image such a way that intruder is not able to trace the information. In this paper a simple visual cryptography based robust digital image watermarking scheme is presented. Watermark Robustness is obtained by using repetition codes and Security of the watermark by visual cryptography. In this method watermark bits are not embedded directly into the cover image. Instead, two shares will be generated using (2,2)visual cryptography. Out of these one share is embedded inside the cover image after encoding and other share is kept secret and used at the time of watermark reconstruction. Hence it is difficult to detect or reveal water mark from watermarked image by unauthorized user. The Performance of proposed scheme is studied for five different watermark images without coding, with (3,1) and (5,1) repetition codes for various noise densities of Salt and Pepper Noise (SAP Noise). For these cases i) Normalized Correlation (NC) between original and reconstructed watermark and ii) Bit Error Rate (BER) in reconstructed watermark is computed. It is seen that the variance of NC or BER is very small and less than 10. This implies that NC and BER are almost independent of watermark. The reconstructed watermark is found to be of acceptable quality even with SAP noise up to 0.5.