For thousands of years, human beings have been relying on keys, documents, passwords and other traditional media and specific knowledge to verify someone’s identity. However, as the society is getting more and more informatized, the limitations and shortcomings of such traditional forms of identity authentication are more obvious. Likewise, traditional identification techniques and methods can not meet the needs of today’s rapid developing society. Whenever the items used for identification are lost or deciphered, the social harm is serious. The high-security and reliable automatic identification technology becomes an urgency.

In response to the urgent need of the society, all kinds of new automatic identification technologies have emerged. So far not many ?have solved the limitations and shortcomings of the traditional identification technologies or reached the purpose of achieving accurate identification. Many try to improve the identification technology instead of going back to the original goal of positively recognizing individuals.

In terms of identity authentication procedure, the traditional identification methods transfer the identity into specific items identification media, such as keys, documents, user names and passwords. However, these items can be easily be lost, counterfeited or forgotten. Such traditional identification methods can not distinguish the real owner of a particular item from the counterfeiters. Once someone with ulterior motive gets the information or media, they would enjoy the same authority as the real owners, which may jeopardize the safety of property and people.

The biometric identification technology only recently emerged. Its purpose is to fundamentally solve the problem of the traditional technologies and is gradually being accepted in the market. Biometric identification technology is a new technology, adopting individual physiological and behavioral characteristics to carry out personal identification. These individual characteristics include recognition of the face, fingerprint, iris, voice, retina and other biological characteristics, gesture of signature, the way of walking, the strength of clicking the keyboard as well as other behavioral characteristics which are called biological characteristics. The reason for being used as identification of individuals is that they are universal for each individual and vary from person to person. Besides, they do not change as time goes by. Compared with the traditional identification technologies, the biometric recognition technology based on the biological characteristics enjoys many more advantages. They can not be lost, forgotten, counterfeited or stolen. They are available anytime, anywhere. As the biometric identification technology undergoes rapid develops, it will become an important technology for future identification.

Among those biological characteristics, human face is the most natural and visual for identification. It is in accordance with humans’ physiological visual habit as human beings recognize others by their faces. Face recognition systems have no highly demanding requirements for image acquisition devices. Even common cameras can be used for face recognition. Therefore, it is low-cost and easily integrated in security systems. With the development of face recognition technology, its accuracy and reliability is greatly improved. Face recognition systems with its significant technological advantages will become the most potential means of biological identification for today’s society.

Human face recognition is the most natural, visual and potential way of biological identity recognition, meeting the humans’ physiological visual habit, just like human beings recognize others by their faces.

The capability of face recognition is restricted by many environmental conditions such as the variation of light, expression, age and accessory, among which light variants are the most crucial influencing factor. The traditional face recognition technique is based on capturing images under visual light. When the environmental light changes, the effect of recognition drops dramatically and fails to meet the real needs. The capability to adapt and control the outside lighting environment is the key technological bottleneck restricting the popularity of human face recognition technology today.