This paper presents an overview of the main topics related to biometric security technology, with the main purpose to provide a primer on this subject. Biometrics can offer greater security and convenience than traditional methods for people recognition. Even if we do not want to replace a classic method (password or handheld token) by a biometric one, for sure, we are potential users of these systems, which will even be mandatory for new passport models. For this reason, to be familiarized with the possibilities of biometric security technology is useful. 1 This work has been supported by FEDER and MEC, TIC-2003-08382-C05-02 Distinctiveness: Any two persons should be different enough to distinguish each other based on this characteristic. Permanence: the characteristic should be stable enough (with respect to the matching criterion) along time, different environment conditions, etc. Collectability: the characteristic should be acquirable and quantitatively measurable. Acceptability: people should be willing to accept the biometric system, and do not feel that it is annoying, invasive, etc. Performance: the identification accuracy and required time for a successful recognition must be reasonably good. Circumvention: the skill of fraudulent people and techniques to fool the biometric system should be negligible. Biometric traits can be split into two main categories:Physiological biometrics: it is based on direct measurements of a part of the human body. Fingerprint, face, iris and hand-scan recognition belong to this group.Behavioral biometrics: it is based on measurements and data derived from an action performed by the user, and thus indirectly measures some characteristics of the human body. Signature, gait, gesture and key stroking recognition belong to this group. However, this classification is quite artificial. For instance, the speech signal depends on behavioral traits such as semantics, diction, pronunciation, idiosyncrasy, etc. (related to socio-economic status, education, place of birth, etc.) [2]. However, it also depends on the speaker's physiology, such as the shape of the vocal tract. On the other hand, physiological traits are also influenced by user behavior, such as the manner in which a user presents a finger, looks at a camera, etc.
VERIFICATION AND IDENTIFICATIONBiometric systems can be operated in two modes, named identification and verification. We will refer to recognition for the general case, when we do not want to differentiate between them. However, some authors consider recognition and identification synonymous.