Historical information

The carte de visite, English: 'visiting card', was a format of small photograph which was patented in Paris by photographer André Adolphe Eugène Disdéri in 1854, although first used by Louis Dodero.
Each photograph was the size of a visiting card, and such photograph cards, in an early form of social media, were commonly traded among friends and visitors in the 1860s. Albums for the collection and display of cards became a common fixture in Victorian parlors. The popularity of the format and its rapid uptake worldwide were due to their relative cheapness, which made portrait photographs accessible to a broader demographic, and prior to the advent of mechanical reproduction of photographs, led to the publication and collection of portraits of prominent persons. It was the success of the carte de visite that led to photography's institutionalization.
https://en.wikipedia.org/wiki/Carte_de_visite

Physical description

Three B&W male portraits undated
a. R.O. Henderson, studio photo with pillar, by Johnstone O'Shannessy & Co.
b. Henry Jackson, head portrait in Dec. 1866, Photographed by Batchelder, Pall Mall, Sandhurst
c. Mr. Jackson oval portrait facing left; photographed by N White, photographer, Mitchell Street, Sandhurst.