I am trying to develop a mechanism for automatically scanning documents which involves picking up pages or sheets of paper. I need a method for determining whether an extra page has been picked up. I have considered using a beam of light that would pass through the page or pages and a sensor on the other side of of the page could determine how much light has passed through. Less light passing through would indicate that the machine has picked up an extra page. What I am wondering is how would this work for very thick or glossy paper like the kind in a magazine? Would visible light be absorbed completely by the paper, and if so what other forms of energy could pass through such paper? Would infrared radiation be a possibility?