Techniques and technologies for tracking a face with a plurality of cameras wherein a geometry between the cameras is initially unknown. One disclosed method includes detecting a head with two of the cameras and registering a head model with the image of the head (as detected by one of the cameras). The method also includes back projecting the other detected face image to the head model and determining a head pose from the back-projected head image. Furthermore, the determined geometry is used to track the face with at least one of the cameras.