He is wearing a Fusiliers shoulder title and I am leaning towards it being Royal Fusiliers rather than Northumberland Fusiliers because of the shape of the letter to the left of the grenade. The close up of the button is also more like the Royal Fusiliers button as it appears to have a circular blank space around its edge. The photograph is signed: "yours Algy", which I take to be a shortened version of Algernon.
I can find only two officers in the Royal Fusiliers during the Great War with the name Algernon. They are:
Algernon Oswald Coggin, who was killed in action on 27th October 1916, aged 24. He was the son of Edith Coggin, of 247, Neville Road, Forest Gate, London.
Algernon Horace Jackson who was commissioned as a Second Lieutenant in October 1914 and who arrived in France on 16th November, 1915. His home address is listed on his medal card as 164 Gwyder Street, Cambridge.
All well and good except that the photograph was framed in Belfast and I can find no link between either of these two officers and Belfast or indeed the Royal Fusiliers and Belfast. There were no Officer Cadet Battalions based there either.
Am I barking up the wrong tree or is the photograph of one of the two men that I have mentioned?