Image feature extraction includes extracting an cutout image that includes an object from an original image; filling borders of the cutout image with a single color as a background to generate a minimum square image; resizing the minimum square image into a resized square image having a first predetermined size; dividing the resized square image into sub-image blocks having a second predetermined size; computing luminosity derivatives of neighboring pixels in horizontal, vertical, positive 45°, and negative 45° directions for the sub-image blocks; obtaining a quintuplet characteristic vector for the sub-image block; and forming an image characteristic vector of the original image using the quintuplet characteristic vectors of the sub-image blocks.