Input: a marked code with the secret message , the length of the secret message , and random seed
Output: the secret messages
Step 1: determine the center of the mini program code and the length of each module
Step 2: establish a coordinate system and store module coordinates of encoding region in an array
Step 3: determine the embedded region and the start modification module based on and the random number generated by random seed
Step 4: read the module pixel of the marked code from the start modification module; if the module is white, the secret message is 0; otherwise, it is 1
Step 5: repeat step 4 until all the secret bits have been extracted
