1. A method comprising the steps of providing a vending machine having a plurality of product dispensing locations from which products are moved to a product retrieval location, monitoring the intensity of light at an array of pixels, detecting a change in the intensity of light at pixels in the array of pixels upon movement of a dispensed product from a product dispensing location to a product retrieval location, and providing a control signal in response to detection of a change in the intensity of light at pixels in the array of pixels, wherein said step of detecting a change in the intensity of light at pixels in the array of pixels includes determining whether or not the intensity of light at one of the pixels in the array of pixels is greater than a predetermined intensity.