A judging method including: obtaining an image of a subject for judgement as a subject image by using an imaging device; judging, by comparing the subject image with a registered image, whether a difference between the subject image and the registered image is greater than or equal to a first threshold; extracting a feature quantity from the subject image and a feature quantity from the registered image if the difference is judged to be greater than or equal to the first threshold; extracting a region of the subject image where a difference in the feature quantity between the region and an associated region of the registered image is greater than or equal to a second threshold; and displaying by a display device the extracted region in the subject image.
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