1. A computer-implemented method comprising: capturing, using a light sensor, a plurality of images of a subject including a view of an eye of the subject while changing one or more parameters at different times during the capturing and according to a pattern; determining a behavioral metric based on, at least, detected movement of the eye as the eye appears in a plurality of the images, wherein the behavioral metric is a measure of deviation of detected movement and timing from expected movement of the eye based on the pattern; and rejecting or accepting the images based on, at least, the behavior metric.