Multi-Threshold Visual Secret Sharing

Visual cryptography (VC) has been developed extensively based on its practicability. These schemes can encode a black-and-white secret image into several shadow images, and, by stacking a certain number of shadow images, can retrieve the secret image through the human visual system. In this paper, we employ Hsu et al.’s ideal multi-threshold secret sharing scheme based on monotone span programs (MSP) to propose a multi-threshold visual secret sharing scheme. In our scheme, there are multiple secret images to be shared among a group of shadow images, and we can define the corresponding multiple access structures for different secret images. Accordingly, different qualified subsets of the group of shadow images can recover the different secret images by stacking them. The experimental results demonstrated that the proposed scheme is feasible and practical.