Origins of Motion Pictures - Inventing Entertainment: The Early Motion Pictures and Sound...

On August 24,1891, Thomas Edison patented his motion picture camera.
From the article:

"Edison's assistant, William Kennedy Laurie Dickson, was given the task of inventing the device in June 1889, possibly because of his background as a photographer. Charles A. Brown was made Dickson's assistant. There has been some argument about how much Edison himself contributed to the invention of the motion picture camera. While Edison seems to have conceived the idea and initiated the experiments, Dickson apparently performed the bulk of the experimentation, leading most modern scholars to assign Dickson with the major credit for turning the concept into a practical reality. The Edison laboratory, though, worked as a collaborative organization. Laboratory assistants were assigned to work on many projects while Edison supervised and involved himself and participated to varying degrees. Ultimately, Edison made the important decisions, and, as the "Wizard of West Orange," took sole credit for the products of his laboratory.

The initial experiments on the Kinetograph were based on Edison's conception of the phonograph cylinder. Tiny photographic images were affixed in sequence to a cylinder, with the idea that when the cylinder was rotated the illusion of motion would be reproduced via reflected light. This ultimately proved to be impractical.

The work of others in the field soon prompted Edison and his staff to move in a different direction. In Europe Edison had met French physiologist Étienne-Jules Marey who used a continuous roll of film in his Chronophotographe to produce a sequence of still images, but the lack of film rolls of sufficient length and durability for use in a motion picture device delayed the inventive process. This dilemma was aided when John Carbutt developed emulsion-coated celluloid film sheets, which began to be used in the Edison experiments. The Eastman Company later produced its own celluloid film which Dickson soon bought in large quantities. By 1890, Dickson was joined by a new assistant, William Heise, and the two began to develop a machine that exposed a strip of film in a horizontal-feed mechanism.

A prototype for the Kinetoscope was finally shown to a convention of the National Federation of Women's Clubs on May 20, 1891. The device was both a camera and a peep-hole viewer, and the film used was 18mm wide. According to David Robinson who describes the Kinetoscope in his book, From Peep Show to Palace: The Birth of American Film, the film "ran horizontally between two spools, at continuous speed. A rapidly moving shutter gave intermittent exposures when the apparatus was used as a camera, and intermittent glimpses of the positive print when it was used as a viewer--when the spectator looked through the same aperture that housed the camera lens."

A patent for the Kinetograph (the camera) and the Kinetoscope (the viewer) was filed on August 24, 1891."