United Kingdom
Royal Horse Artillery

Carte-de-Visite, no studio backmark

Major, Royal Horse Artillery

This photo shows an Officer whose rank is indicated by a Star ; his cuffs can't be seen, but given his age, there's no reason to think he'd be a Cornet - so he has the rank of Major.
The Regimental Rank of Major had been abolished in the Royal Artillery on 6th November 1827 ; it was reinstated in 1872.
The CDV could be pre-1872 though, and this gentleman having a Brevet of Major.

He is wearing the Campaign Medal for the Indian Mutiny.