The applications of vision-based face tracking to HCI are evident. Face tracking based program control can be used as a hands-free alternative and/or extension to conventional pointing devices such as mouse, joystick, track pad or trackball. This can be used, for example, to switch the focus of attention in windows environment. Vision-based perceptual user interfaces can also be used to control commercial computer games, immersive 3D worlds and avatar-like computer generated communication programs. For users with physical disabilities, this technology offers a way of controlling an onscreen cursor by moving their heads. Finally, face tracking has applications in security industry, where it is a prerequisite for the next step of face recognition, in video-conferencing, where it can be used to correct the gaze direction, and also in video-coding and content-based image retrieval.