The backing is just brown paper and has a postcard-size piece of paper stuck on it, on which is written his name, date of attestation and date of discharge.
The picture was hanging at my GF's house until his death in 1966. GF had eight children. The picture now belongs to the son of GF's eldest daughter. I think the handwriting on the card belongs to the daughter of GF's second daughter. I think another cousin (I've got loads, want to borrow any?), son of GF's fourth daughter, has a photo of GGF in uniform, and has been promising for years to "look stuff out of the loft", but keeps failing to do so.
In fact, I'm going to ring him now and chivvy, chivvy.