I. Introduction
Biometric technology utilizes the biological characteristics of human bodies or behaviors as identification or verification features. The frequently used biometric features include face, fingerprint, voiceprint, and iris recognition. And the signature, handwriting, and walking type belong to the behavioral features. The fingerprint recognition is the most popular adopted in our daily lives. However, the sweat and the dust may reduce the accuracy sometimes. In face recognition system, it is not necessary to have physical contact with the machine and the image can be captured naturally by using a video camera. This makes face recognition a very convenient biometric identification approach. The face detection is an important preprocessing step for face recognition.