The original photo shows the soldier wearing a slouch hat with the common ostrich feather plumes of a Mounted Infantry unit.
By which I mean, a unit which manoevres on horseback but dismounts to fight [unlike cavalry who are meant to stay mounted].
Any unit called ...Mounted Infantry or ... Light Horse or ...Scouts would do... BUT with the exception of the South African Light Horse, who wore the plumes of the sakabula [long-tailed widowbird (Euplectes progne)] in their hat.
The past is not dead. In fact, it's not even past.