The mystery photograph

I was looking at an old brooch this morning that belongs to my mother. I noticed something round and blurry on the reverse. It turns out to be a photograph of a man under a hinged piece of glass. I wonder if these brooches - round enamel with a pearl cluster centre  on the front and a hidden photo compartment in the back, were commonplace. More importantly I wonder who the man is as I do not recognise him.

I am hoping it might be a photograph of my grandfather. Nobody knows what he looks like as we can find no photograph of him. He died when my mother was 7 from the after effects of being in the trenches in the First World War. My mother only remembers him being shut away, in bed, suffering from what I think was kidney failure. On good days he painted posters for Boots the chemist and did his doctor's book keeping in exchange for treatment (no NHS in those days.)

The man in the photograph has wavy thick light coloured hair and a nice, quite handsome face. It's such a tiny photograph. It must have been treasured once for the wearer to want to have it pinned close to her heart.