A camera (12, fig. 1) captures images of objects (24, fig.1) on a conveyor (2, fig. 1). A processing system determines the outline 28 of the object and a contour device, in a number o steps, successively reduces the outline to produce progressively smaller outlines 32, 34, 36 until one or more central regions 42a, 42b are identified. Subsequently the outlines of the one or more central regions are successively enlarged equally around their peripheries, using the same number of steps, to produce an outline of the one or more products 44, 46. The method may be used to detect overlapping crisps or snacks, and the information then be used to control product flow by altering the speed of the conveyor or power of a microwave.
