In our daily life, credit cards, bank passbooks, Twitter accounts or Internet accounts etc., are all protected by passwords which have been targeted by hackers and criminals. Therefore, the traditional authentication systems which authenticate personal identities simply by objective markers or by specific knowledge are facing a huge security challenge.
People find that some of the human biological characteristics cannot be replicated easily and quickly under nowadays science technology. Therefore, biometrics technology becomes the new hope. With biometrics, people hope to overcome the challenges that the current security system is facing. The physical characteristics that are used for identification have to be unique and stable. Researches and experiments indicate that human face, fingerprint, palm vein, voice, iris and DNA etc. are relatively unique and stable normally, i.e. each of these characteristics is different from each other.