Abstract: A video image based control system including a video camera scans a field of view and generates video signals representing the captured image of the field of view. The video signals are applied to a digitizer which converts the video signal into digital information. The digital information is conveyed to a computer and stored. The computer then performs an AND function on the stored digital information and on bitmaps stored in the computer memory associated with predefined areas of interest in the field of view of the video camera to determine whether a participant in the field of view is positioned so that at least a portion of the participant is located in an area of interest. If the participant is detected as being within an area of interest, the computer determines the proportion of the area of interest obscured by the participant and generates a control signal having a value dependant on the proportion of the area of interest obscured by the participant.