Abstract: A registration system for a packaging machine, which machine seals tray tops with thermoplastic film. The trays are carried through the machine on a moving conveyor and the sealing film is fed in a ribbon from a feed roll to move in a position above the line of trays carried on the moving conveyor. The film ribbon carries printing or decorations, in repetitive segments, which must each be centered on a respective tray top when the film is sealed thereto. Repetitive registration marks carried on the film ribbon indicate the position of each film segment as it moves toward a heat seal station. The registration marks are optically sensed in time with the timing pulses of the packaging machine. When miss-registration is sensed the film position, relative to the leading edge of the tray adjacent to and next to enter the heat seal station, is indexed forward a predetermined increment by a downward operating blade and then a heat bar contacts the film and tacks it to the leading edge of that tray.