Biometrics refers to the automatic identification of human beings based on their physical and/or behavioral characteristics (Bio = life + Metrics = measurement).
These characteristics present some specific properties such as, uniqueness and persistency, making them suitable for this kind of task. Examples of physical characteristics include among others: fingerprints, face, iris, retina, and hand geometry. On the other hand, examples of behavioral characteristics include: signature, voice, keystroke dynamics, etc.
Traditionally, authentication methods are divided into three main groups:
The user possesses a physical and portable device which contains the users identity. Examples of such devices include bankcards, driver's licenses, passports, etc.
These methods are based on a user's knowledge characterized by its secrecy. Examples include passwords, PINs, etc.
The user submits to the system his physical and/or behavioral characteristics. As a result, the individual is either accepted as a valid user or is rejected.
Furthermore, an automated biometric system may opperate in two different modes: recognition and identification. In the former mode, the system authenticates a claimed identity by comparing an input biometric characteristic with its theoretical corresponding template. In the latter, the system does not receive a claimed identity and searches therefore an entire database for a match.