| 摘要 |
PROBLEM TO BE SOLVED: To surely detect a watermark. SOLUTION: A watermark read from a watermark pattern holding memory 32 is supplied to an evaluated value calculation device 31-1 with a shift amount 0, which is supplied to the evaluated value calculator 31-2 by being shifted for the shift amount (i) and supplied to the evaluated value calculator 31-3 by being shifted for the shift amount (j). In the evaluated value calculator 31-1, an evaluated value is calculated by using a watermark pattern which is not shifted. In the evaluated value calculators 31-2 and 31-3, the evaluated value is computed by using the watermark pattern shifted for the shift amount (i) or the shift amount (j). An evaluated value comparator 33 sets the evaluated value of the intermediate value among the evaluated values outputted by the evaluated value calculators 31-1-31-3 as a standard evaluated value. The evaluated value comparator 33 compares the absolute value of a difference between the reference value and the evaluated value of the shift amount 0 with a prescribed threshold and discriminates that the watermark has been added, when absolute value is larger than the threshold. |
