from Terry Barrett, Criticizing Photographs
Descriptive photographs: All photos describe, at some level, but some are not intended to do anything more than that.
Explanatory photographs: Your driver's license photo describes; Eadward Muybridge's photos of a horse running explained. Social scientists use photos to explain as well - e.g., visual anthropology. These photos are intended to document a way of life.
Interpretive photographs: These do not strive for scientific accuracy, as explanatory photos do, but rather are personal or subjective interpretations. They tell us how things are, but there is an interpretation of how things are imbedded in the photo.
Ethically evaluative photographs: These photos make ethical judgments. They praise or condemn aspects of society.
Aesthetically evaluative photographs: These make judgments not about social issues but about aesthetic issues. They tell us what is worth aesthetic observation.
Theoretical photographs: These comment on art and the making of art. They raise questions about the making of photos. For example, they may deliberately make fun of ethically evaluative photos.