A Co-cheating Prevention Visual Cryptography Scheme

Participants colluding is an important issue of cheater detectable visual cryptography schemes. Based on a trusty third party, a co-cheating prevention visual cryptography scheme (CCPVCS) is proposed in this paper. Checking efficiency is improved by verifying the truth of several shares simultaneously, with designed special verification shares. Since the scheme idea is different from previous ones, the pixel expansion is small and the recovered secret image is good for viewing.