1. A video signature generation device, for identifying duplicate video content, comprising: a processor that controls the video signature generation device to implement: a visual feature extraction unit which extracts a visual feature of a video based on features of two sub-regions in a single frame in the video; and a confidence value calculation unit which calculates a confidence value of the visual feature based on the features of the two of sub-regions in the single frame, wherein the confidence value calculation unit calculates the confidence value based on a difference between the two sub-regions in the single frame.