Cheating Prevention in Visual Cryptography - Visual Cryptography and Secret Image Sharing - page 283

FIGURE 10.8
HT.
a. For each white pixel in the verification image, the block of vi i created
based on [1 0 0 ... 0] (after corresponding permutation as for generating
the secret shares in step 2).
b. b For each black pixel in the verification image, the block of vi i created
based on [0 1 0 ... 0] (after corresponding permutation as for generating
the secret shares in step 2).
In the decoding phase of the secret image, before stacking transparencies, each
P i checks the stacking result of vi i with T j held by participant Pi j revealing his
own verification image. Figure 10.9 shows an example of an HT scheme.
10.3.3 TCH
In [18], Tsai et al. proposed a cheating prevention scheme, shown in Figure
10.10, images where shares are generated by Genetic Algorithms. TCH adopts
multiple secret images with the same visual meaning. Each qualified subset
only reveals the corresponding reconstructed secret image and the others are
left unknown to potential cheaters. Any participant accepts the decoding re-
sult only if the visually reconstructed secret image is authentic. In TCH, the
fitness function of the Generic Algorithm was designed according to a 2-out-
of-n visual secret sharing scheme. But, it is not guaranteed that the same
quality is obtained because the Generic Algorithm is a kind of heuristic al-