Behavioral-based authentication methods perform the identification task by recognizing people's behavioral patterns, such as signatures, keyboard typing, and voice print. The main problem with behavioral methods is that they all have high variations, which are difficult to cope with. To prevent signatures from being altered, the use of laser-engraved, digitally embossed signatures on the card's signature panel has also been considered. On the other hand, while behavioral characteristics can be difficult to measure because of influences such as stress, fatigue, or illness, they are sometimes more acceptable to users and generally cost less to implement. Good examples are speaker recognition systems, as discussed in Chapter 9.

Physiological-based authentication methods verify a person's identity by means of his or her physiological characteristics such as fingerprint, iris pattern (eye blood vessel pattern), palm geometry, DNA, or facial features. In general, traits used in the physiological category are more stable than methods in the behavioral category because most physiological features are virtually nonalterable without severe damage to the individual.