1. A system operable to generate a probabilistic similarity measure based on a first intensity value and a second intensity value of a digital image, the system comprising: a noise characterization module operable to determine noise characteristics of a camera producing the digital image and operable to form a noise curve descriptive of the noise characteristics; and a comparison module operable to calculate a probability of correspondence, based at least in part on the noise curve, for each possible true intensity value of a set of possible true intensity values wherein each of the probabilities of correspondence indicate similarity between the first intensity value and the second intensity value relative to the corresponding possible true intensity value.