Answer by taking a quote from the following article:

Thomas Cowperthwait Eakins (July 25, 1844 - June 25, 1916) was an American realist painter, photographer, sculptor, and fine arts educator. He is widely acknowledged to be one of the most important artists in American art history. For the length of his professional career, from the early 1870s until his health began to fail some 40 years later, Eakins worked exactingly from life, choosing as his subject the people of his hometown of Philadelphia. He painted several hundred portraits, usually of friends, family members, or prominent people in the arts, sciences, medicine, and clergy.

Eakins has been credited with having "introduced the camera to the American art studio". During his study abroad, he was exposed to the use of photography by the French realists, though the use of photography was still frowned upon as a shortcut by traditionalists.  In the late 1870s, Eakins was introduced to the photographic motion studies of Eadweard Muybridge, particularly the equine studies, and became interested in using the camera to study sequential movement. In the mid-1880s, Eakins worked briefly alongside Muybridge in the latter's photographic studio at the University of Pennsylvania in Philadelphia. Eakins soon performed his own independent motion studies, also usually involving the nude figure, and even developed his own technique for capturing movement on film. Whereas Muybridge's system relied on a series of cameras triggered to produce a sequence of individual photographs, Eakins preferred to use a single camera to produce a series of exposures superimposed on one negative. Eakins was more interested in precision measurements on a single image to aid in translating a motion into a painting, while Muybridge preferred separate images that could also be displayed by his primitive movie projector.  After Eakins obtained a camera in 1880, several paintings, such as Mending the Net (1881) and Arcadia (1883), are known to have been derived at least in part from his photographs. Some figures appear to be detailed transcriptions and tracings from the photographs by some device like a magic lantern, which Eakins then took pains to cover up with oil paint. Eakins' methods appear to be meticulously applied, and rather than shortcuts, were likely used in a quest for accuracy and realism.  An excellent example of Eakins' use of this new technology is his painting A May Morning in the Park, which relied heavily on photographic motion studies to depict the true gait of the four horses pulling the coach of patron Fairman Rogers. But in typical fashion, Eakins also employed wax figures and oil sketches to get the final effect he desired.  The so-called "Naked Series", which began in 1883, were nude photos of students and professional models which were taken to show real human anatomy from several specific angles, and were often hung and displayed for study at the school. Later, less regimented poses were taken indoors and out, of men, women, and children, including his wife. The most provocative, and the only ones combining males and females, were nude photos of Eakins and a female model (see below). Although witnesses and chaperones were usually on site, and the poses were mostly traditional in nature, the sheer quantity of the photos and Eakins' overt display of them may have undermined his standing at the Academy. In all, about eight hundred photographs are now attributed to Eakins and his circle, most of which are figure studies, both clothed and nude, and portraits. No other American artist of his time matched Eakins' interest in photography, nor produced a comparable body of photographic works.

How did he introduce the camera
Eakins was more interested in precision measurements on a single image to aid in translating a motion into a painting,