Image Sharing with Steganography and Authentication - Visual Cryptography and Secret Image Sharing - page 442

FIGURE 16.23
The flowchart of Step 4.

Equation 16.16.

Divide each received stego-image SI 0 j , j = 1, 2,..., m, into 2 2
blocks CB 0 1 , CB 0 2 , ..., CB 0 z and denote the four pixels in each
block CB 0 z as C 0 z , D 0 z , G 0 z , and H 0 z as shown in Figure 16.24.

Step 2:

For each stego-image SI 0 j from participant j, j 2 f1; 2;:::;mg ,
perform the following substeps for stego-image authentication.

Step 3:

(a) t = 2, extract the 2-bit check bits from each block CB 0 z , as
shown in Figure 16.25. P 2 = g 0 1 , P 1 = h 0 1 .

(b) Calculate the data for verification according to Equation
16.18.