My guess is Harry Preston. This is based on a letter he wrote in 1916 (just signed Cousin Harry), which I was told had been kept because he died in the war, and that this photo was taken by a Bolton photographer which is where Harry Preston lived.
I haven't been able to find anyone who seems to fit the bill on the CWGC website, and couldn't find a WW1 service record for him. Where do I go to look at the London Gazette?