Watermark detection

The invention claims a method for detecting the same information signal in a watermark method and device for. The method comprises the following steps: For the watermark wi relative to said information signal such as q one image of a plurality of positions k to calculate 24-28 30 the water seal and the information signal dk and correlative value of detecting whether or not in each relative value at least one correlation value exceeds a predetermined threshold value. The step of detecting includes the steps of determining value of each switch dk standard deviation of the sigma d and the threshold value is set as the standard deviation of a given times t. The times of number t of a desired error warning rate leading the t is 0 to detect the watermark; When t is 1 does not detect the watermark.