“…From the perspective of computational complexity, the experimental methods can be divided into three types: robustness verification, algorithm comparisons, and criteria systems. The robustness verification experiments are mainly conducted after the watermarking algorithms have been proposed by performing some attacks [ 8 , 10 , 11 , 17 , 18 , 19 , 20 , 21 , 22 , 23 ]. Normalized correlation ( NC ) [ 10 , 17 , 23 ] and bit error rate ( BER ) [ 17 , 24 ] have been used as the evaluation indexes, which are calculated by comparing the extracted copyright information with the original.…”