For your information:
A carte-de-visite is small albumen print that is mounted on a standard sized 2 1/2" by 4" backing card. The process was patented in 1854 by a Parisian photographer and the style gained their height of popularity in the United States during the Civil War. The were called carte-de-visite, which is French for "visiting card," because their compact size made them perfect for photographic calling cards that could be presented during a social visit. Their standardized size made them convenient for photo album makers and they were easy to trade and collect. These types of photos also served as a way to familiarize Americans with the faces and popular images of politicians and other celebrities. This particular collection of photographs may have been sold as a set or collected individually. They may have been presented to the public as a souvenir of the war or as a memorial. Around 1868, the larger cabinet card photograph became popular and by 1885 had taken over most of the carte-de-visite's market.