The carte de visite was a small photograph, (2.5" x 3.5") mounted on a card, patented in Paris by photographer Andre Disderi in 1854. They became very popular in Europe and then America, especially during the War Between the States, when soldiers and their friends and families could send them to one another in small envelopes
We have a number of them in an album in the relic room at the First White House of the Confederacy, including Confederate President Jefferson Davis, Generals Robert E. Lee, John Breckenridge, John Bell Hood, James J. Pettigrew, Thomas J. "Stonewall" Jackson, Robert Hoke, and John Hunt Morgan.
A second album includes Alexander Stephens, Vice President of the Confederacy, Robert Toombs, General Leroy Pope Walker, Secretary of War, Mallory, Sec. of Navy, Reagan, Postmaster General and a number of Generals, including Albert Sidney Johnston who was killed at Shiloh and General Polk who was killed during J. E. Johnston's Atlanta campaign.
By the early 1870's I read on the internet that the cartes de visite were supplanted by cabinet cards which were a bit larger (4.5" x 6.5") and these remained popular into the early 20th century when Kodak introduced the Brownie camera and home photography became the rage. I remember my Mother had a brownie camera for years and years and I have albums upon albums of shots she took with that little camera.
One of our prize carte de visite at the First White House is one of Jefferson Davis greatly enhanced in value because it was taken by the celebrated photographer, Matthew Brady.