Listen to part of a lecture from an art history class.
So last class we were talking a bit about the history of photography and as I was saying, with the invention of the camera in the mid to late 1800s, for the first time people were able to record realistic images. Up until then, painting, portraits, landscapes, were the way that realistic images were recorded; the image of a person's face, the painting of a mountain range, but with the invention of the camera, now there was this new piece of technology; this machine that took realistic images and this had an enormous effect on painting. One effect was that painters began using photographs as a tool; a tool to help them paint more realistically. Before the camera, it was extremely difficult to realistically depict a moving object in a painting, but now photography was able to capture fleeting moments; freeze them in time and painters were able to use these photographs as a basis for their paintings. For example, the legs of a horse as its running. Photography could now capture the exact position of a horse's legs in midair, which a painter could use to more realistically create a painting of horses galloping. Photography also affected painting in a more conceptual way. The fact that cameras could now perfectly record realistic images led some painters to change their style; to stop painting realistically and adopt a more abstract way of painting. An abstract style enabled painters to contrast their art with photography, to set their art apart from the art of photography. They didn't want their paintings to look anything like photographs. They wanted their art to be more imaginative, more abstract. For example, if a painter were painting people f he or she might not use natural skin tones for the skin and instead paint the people's skin unnatural colors, like green, purple, or blue, which of course is not realistic.