In order to examine the roles and interferences of local and global elements in lightness perception and object recognition processes of photographs with meaningful contents, we examined whether contrast discrimination is a response to spatial configuration properties of photographs, or also a function of conceptual contents. In three experiments we compared contrast discrimination performances of observers, when presented with contrast increments applied to discrete tonal regions in greyscales and in several categories of black-and-white photographs of natural scenes. In Experiment 1, observers performed contrast discrimination in grey-scales by rank-order tasks. In Experiments 2 and 3, trained and novice observers performed contrast discrimination of photographs by sortingtasks. We found substantial differences in response to contrast increments, depending on the region, but no significant effect of category. Nevertheless, low performances in shadow region of grey-scales, significantly improved in photographs due to complexity of configuration. We also found differences in performance between photographs of light and night scene.