John Bodsworth book on 1914-18 uniforms has an interesting section on POW uniforms ( page 397-398 ), which confirms that
the photograph posted by Nick, is that of British POWs.
It does not say in which POW Camp the photographs were taken, and all the men appear to be in good health, well fed, well groomed, and with the photographs all taken against a backdrop as in a posed studio photograph ?
The book states " That jackets had a piece of brown drill material inset into the left arm, whilst similar material was inset into the outer legs of the trousers ". Some POWs also had a label sewn above their uniform left breast pocket showing their POW number.
There are 3 photographs of POWs shown :-
Photo 1. " of 3 British POWs in Germany. The centre figure is wearing the standard pattern of Service Dress, ... He is wearing shoulder titles with a flaming grenade above.. at the same time, he is wearing a Royal Scots cap badge normally worn with a Glengarry. The soldier on the left, is wearing a plain dark blue uniform...with an armlet, while his trousers have a wide stripe sewn down the outside. He is wearing an Essex Regiment cap badge.
The soldier on the right is wearing a different jacket,( again with an armband ), and on his cap, he appears to be wearing an Argyll and Sutherland Highlanders collar badge. "