Most people can tell with a single glance whether an image is a photograph of a real scene, of a painting, or of some noise function. Moreover, it is generally easy to tell the general nature of the scene ? whether it is of a coast, a forest, some hills, or a city ? as well as often which specific location is depicted. Many people can even tell what style of photography or painting is involved and sometimes even the specific photographer or artist. This is because artworks and natural images exhibit statistical regularities that the human visual system has evolved to exploit. Understanding which regularities tell us about the media (e.g., photograph, watercolor, oil), style, scene, artist, and so forth of a picture can help us understand more about humans and can help in a wide variety of image synthesis and analysis techniques.