1. A computing system, comprising: a photometric stereo imaging system with three light sources to capture multiple images of a paper; a storage to store paper classification information related to three-dimensional statistics of paper types; and a processor to: determine a description of the three-dimensional characteristics of a paper based on images of the paper captured by the photometric stereo imaging system; determine statistical summary information related to the three-dimensional characteristics description; and classify the paper based on a comparison of the statistical summary information to the stored paper classification information.