Art: Usually they're appealing to the viewer and can stir up some emotion.
War: Pictures of battles or their aftermath that show people what's really going on.
Digital Truth: Photos that are altered to show something different than the actual photo.
Presidential Image-making: Casual or formal pictures of the President.
Advertising and Persuasion: They advertise a product and make it seem appealing.
Social Change: They show bad conditions in hope that when people see them they'll try to make change.
Cultural Identity: They show the good and bad times of people of different cultures.