In this chapter, I review some basic statistical properties of photographic images, as observed empirically, and describe several models that have been developed to incorporate these properties. I give some indication of how these models have been validated by examining how well they fit the data, but the true test usually comes when one uses the model to solve an image processing problem (such as compression or denoising). I show some simple denoising examples to give an indication of how much performance gain one can obtain by using a better statistical model.