appearance within the kind of visual environments in which the tracker is operating then it is not possible to build a unique u201c model u201d for that target once a model of the target 106 a is generated a controller 118 is then instructed by the tracking system to control the ptz motors 108 to move the camera to keep the selected target 106 centered in the field of view of the camera 102 such controllers are also well known in the art the controller 118 like the tracking system 116 is preferably implemented by software contained on a peripheral device on the computer 114 two general approaches for controlling the camera 102 that are widely used in the prior art include a discrete approach in which the camera 102 is moved from time to time to keep the target 106 centered and a continuous approach in which the camera 102 is moved to keep the target 106 continuously centered whichever approach is used to control the camera 102 the results of which are fed to the controller 118 which determines the amount of camera movement necessary to keep the target 106 centered in the field of view of the camera 102 the controller 118 outputs an appropriate signal to the ptz motors 108 of the camera 102 to carry out its instructions to.