Photography, first shown in 1834, revolutionized the way painters saw the world.  Several artists, such as Degas and Caillebotte, experimented with photography and were friends of photographers.  It is telling that the first Impressionist exhibition was organized primarily by Degas and held at the house of photographer Felix Nadar, (type Nadar for Artiste in the database). Photography mediated the study of every day scenes rather than the past and mythology, and helped artists better understand the use of light as well as the study of movement "frozen in one instant".

Edgar Degas
Nude Woman Drying Herself c1884/86

These two works show how photography enabled artists to better understand the nature of light and to experiment with light in their art.

The study by Degas is influenced by photo--although"monotonal" studies (e.g. black and white or sepia on off-white) had been practiced in art for centuries.  The treatment, however, is more like a photographic print, if not a photo negative.  Degas himself practiced photography in the early 1890s. There is a series of photographs by Degas of ballerinas where he has developed the photograph so that positive and negative are experimented with in the same photograph. (Kendall, Richard; Degas, beyond Impressionism, p 37).

Gustave Caillebotte  
Paris Street; Rainy Day 1886/87

The following painting by Caillebotte, shows the influence of photography in terms both of theme and the study of light.  Photographers of the time often shot urban scenes of the changing Paris.  Caillebotte strives to capture "a rainy instant" of the newly designed Paris.  He uses photo to create a hyperreality:  the street scene could be real, although perspective is skewed. The reflections off the newly  cobbled streets  of Paris reflect the color of the sky.  The busy bustling figures under the umbrellas walk hastily to their destination.  

Based on photography, Caillebotte creates the illusion of reality through painting.

Other artists were also influenced by photography. For example, Lautrec had several photos taken of himself in costume, alone and with his friends. There are several photographs of Lautrec in his studio. Many of Lautrec's compositions, such as Ballet Dancers, show a dynamism that would hardly have been achieved without the use or knowledge of photography.

Courbet was influenced by photography. He allowed himself to be photographed and participated in photo shoots for open air scenes that included peasant life and the working class. He was a supporter of Felix Valloton's photographic realism. Valloton and Courbet shared a common interest: both intensively used the female body as subject. Courbet would incorporate his female nudes in naturalist landscapes. Vallotton used stock images of nudes as a substitute for live models.