Biometric technologies use physical characteristics, such as voice tone or hand shape, to identify people automatically. Behaviors, such as handwriting style, can also be used by computers in this way. The term “identify” is used here quite loosely. There is actually nothing in your voice, hand shape or any biometric measure to tell the computer your name, age or citizenship, or to establish your eligibility to vote. External documents (passport, birth certificate, naturalization papers) or your good word establishing these facts must be supplied at the time you initially present yourself to the biometric system for “enrollment”. At this initial session, your biometric characteristic, such as an eye scan, is recorded and linked to this externally-supplied personal information. At future sessions, the computer links you to the previously supplied information using the same physical characteristic. Even if the biometric system works perfectly, the personal data in the computer, such as your voting eligibility, is only as reliable as the original “source” documentation supplied.
Once the computer knows your claimed identity, it can usually recognize you whenever you present the required biometric characteristic. No biometric identification system, however, works perfectly. Problems are generally caused by changes in the physical characteristic. Even fingerprints change as cuts, cracks and dryness in the skin come and go. It is far more likely that the computer will not recognize your enrollment characteristic than link you to the characteristic of someone else, but both types of errors do occur.