Abstract: A fingerprint image is processed from its original gray tone image to a binary (black and white) image. The "ridge" skeletal image is formed of the black portions of the binary image, being derived from the ridges of the fingerprint. A separate "valley" skeletal image is formed of the white portions of the binary image, being derived from the valleys interposed between the ridges. Ridge minutiae are detected from the ridge skeletal image and processed to eliminate apparently inappropriate minutiae. Separately, valley minutiae are detected from the valley skeletal image and processed to eliminate apparently inappropriate minutia. Then the ridge and valley minutiae are processed together. Only those ridge minutiae that can be correlated locally with individual valley minutiae survive to be passed to a fingerprint matcher.