Survey of Cheating Prevention Techniques in Visual Cryptography

Visual cryptography (VC) is a technique of encoding a secret image into share images such that stacking a sufficient number of shares reveals the original secret image. Shares are generally presented in transparencies. So each participant holds a transparency. The original secret image is recovered after superimposing the transparencies one to other. Basically, the performance of visual cryptography scheme depends on different measures, like pixel expansion, security, contrast, computational complexity, accuracy, share generated, number of secret images and type of secret images encrypted by the scheme. Most of the prior research work on VC focuses on improving two parameters: pixel expansion and contrast. Visual cryptography (VC) has numerous applications, such as authentication and identification, steganography, and image encryption. Horng et al. showed that cheating is possible in VC, where some participants can betray the remaining participants by fake transparencies. So, designing cheating-prevention visual secret-sharing (CPVSS) schemes has been proposed by many researchers to overcome cheating problem from existing VC. Intent of this paper is on study and performance analysis of the cheating prevention visual cryptography schemes and cheating problem in VC and extended VC.