I've just checked the Army Dress Regulations for Officers 1913, and nowhere does it authorise the wearing of a Sam Browne with Full Dress or Undress Uniform, which is what this chap is wearing. The only time I've come across this is during sword drill, or rehearsal parades (eg at Sandhurst) where swords are carried.
There is a reference on Wikipedia (fourth paragraph of
this section of the article) which says the wearing of the Sam Browne was authorised for officers and WO1s by the Australian Army 'on ceremonial occasions' but at no point does the article or the
source document mention either Full Dress, Undress or No1 uniform, so I think that's a red herring. That statement would also apply to the British Army where No2 dress was worn on parade.
Given that this would appear to be an unauthorised form of dress, perhaps the photograph is not of a real soldier/officer, or is some sort of fancy dress or stage costume.
