Cartes de visite.

The carte de visite, sometimes hyphenated as carte-de-visite, was a type of small photograph which originated in France in the late 1850s and became immensely popular in both Europe and the United States. It consisted of a thin paper photograph (usually an albumen print) mounted on a thicker paper card, about the size of a modern-day playing card. Their popularity led to the production of cards with photographs of notable people, which were collected and traded.

From the guide to the Cartes de visite Collection, 1859-1900, (Special Collections Research Center, Syracuse University Libraries)