TOPIC:

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.

If they are, then the photograph must be post war.

djb wrote: RSW,

That's an interesting picture.

It could possibly be a QSA and KSA under the bandolier but there is too little to confirm this.