Watermarking-Based Transparency Authentication in Visual Cryptography

This paper proposes two transparency authentication schemes used in visual cryptography, which are based on watermarking techniques. In the first scheme, a secret image can be perceptible when stacking two transparencies. In addition, another watermark image is visible when shifting one transparency to an appropriate position and stacking it with the other transparency. In the second scheme, both the secret image and the watermark are of the same size, while in the first scheme, the watermark is half of the size of the secret image. No computer aid is needed in decryption in the first scheme while simple computation is required in the second one. The secret image and the watermark are encrypted at the same time in the two schemes. Experimental results demonstrate the two schemes are effective and practical.