1. A feature extraction method for extracting a feature description from an image of a subject, the feature extraction method comprising the steps of: capturing the image with an image capturing device; electrically creating a filter bank from said image; electrically creating a maximum brightness image from said filter bank; electrically setting a circular image region of said maximum brightness image, and setting a center Cc and a radius Rc of the circular image region; electrically projecting a pixel in the maximum brightness image in a three-dimensional space having axes representing (a) a ratio between a distance L D between a pixel position (x, y) of the pixel and said center Cc, and said radius Rc, (b) a brightness value F D (x, y) of the pixel, and (c) the total of the difference between the brightness value F D of the pixel and the brightness value of a nearby pixel; and electrically creating a frequency histogram from the pixels projected in said three-dimensional space.