When retrieving an image from an archive of stored images that is similar to an inputted image, an image-processing apparatus (200) extracts more than one characteristic point from the inputted image (S504), computes a characteristic amount for the characteristic points thus extracted (S505), and evaluates the fluctuation in the characteristic amount when a prescribed alteration is applied to the inputted image (S506). The image-processing apparatus selects a characteristic point from among the characteristic points thus extracted from the inputted image, and retrieves (S508) a stored image that is similar to the inputted image, in accordance with the characteristic amount of the characteristic point thus selected.