1. A method comprising, in combination: (a) a first set of one or more light sources illuminating a surface with incoherent light; (b) a second set of one or more light sources illuminating the surface with coherent light; and (c) one or more cameras capturing images of the surface while the surface is illuminated with the incoherent light and while the surface is illuminated with the coherent light; and (d) one or more computers (i) taking, as input, data indicative of or derived from the images, (ii) determining a classification of the surface, and (iii) based on the classification, outputting signals to control an I/O device, such that what content is displayed by the I/O depends, a least in part, on the classification.