There are four types of fingerprint scanner: the optical scanner, the capacitance scanner, the ultrasonic scanner, and the thermal scanner. The basic function of every type of scanner is to obtain an image of a person’s fingerprint and find a match for it in its database. The measure of the fingerprint image quality is in dots per inch (DPI).
Human fingerprints are practically unique, which is why they’re successful at identifying individuals. It’s not just law enforcement agencies that collect and maintain databases of fingerprints. Many types of occupations that require professional licensing or certification (e.g. financial advisors, stockbrokers, real estate agents, teachers, doctors/nurses, security, contractors, etc.) mandate fingerprinting as a condition of employment. It’s also typical to provide fingerprints when having documents notarized.