Fingerprint scanners capture digital images of fingerprints and compare them to other fingerprint images on file. There are two main types of fingerprint scanners: optical scanners and capacitive scanners.
Optical fingerprint scanners have a charge-coupled device, or CCD, similar to the one found in digital cameras. The CCD is comprised of several light-sensitive diodes that produce electrical signals and record pixels when exposed to light. During the scanning process, light-emitting diodes illuminate the skin and light-sensitive diodes record light and dark pixels depending on the amount of light reflected by each point on the skin. Ridges reflect more light and are recorded as light pixels, whereas valleys reflect less light and are recorded as dark pixels. Together, these pixels form a fingerprint image.
Capacitive fingerprint scanners use electrical current instead of light to capture fingerprint images. They have semi-conductor chips that are made up of several tiny cells, each of which is comprised of two conductor plates. During the scanning process, the ridges on the skin connect the conductor plates and complete the circuits. The scanner distinguishes the ridges from the valleys and generates a fingerprint image by sensing the voltage output in the different cells.
Fingerprint scanners come with software that recognizes and compares distinctive features in fingerprint images using complex algorithms. These features, called minutiae, typically include points where ridge lines end or split. If the software finds the same minutiae pattern in two fingerprints, they may be a match.