the doorway the iris capture may be triggered at different standoff distances for users with different heights depth sensor 26 may be installed at various positions and orientations depth sensor 26 may be positioned very close to nfov camera 22 to allow for a more compact design nir illuminator 24 can be placed at any location so long as it illuminates capture volume 40 system 20 can be applied to other possible settings in which depth sensor 26 is used for example camera 22 may be in the form of a high speed high performance video camera alternatively camera 22 may have a fixed focus or adjustable focus based on the distance between the camera and the user it is also possible for camera 22 to include pan tilt capabilities in order to further enlarge the capture volume an operational block diagram of system 20 is illustrated in fig2 the three dimensional information measured by depth sensor 26 may be used in various ways within system 20 first face detection and tracking 46 may be performed on the up sampled intensity images 48 captured by depth sensor 26 the three dimensional position of the eyes may then be estimated from an upper portion of the detected face depth maps the next eye location for the moving subject may be predicted accurately in real time for example time rates of change of the three dimensional position.