Abstract: Bottles transparent to a laser beam are molded with marks on a wall thereof. The marks serve to identify each bottle with its respective mold. The bottles are rotated and moved in a procession through an inspection area where a laser beam is directed through the wall of each bottle so that the beam strikes each of the marks. Each mark causes the laser beam to spread as the beam strikes the mark and passes through the bottle. As the laser beam emerges from the bottle, the beam is directed to a sensor which generates a digital output signal corresponding to the distribution of the marks on the bottle. Any bottle may be ejected from the procession according to the sensor output.