If a picture tells a story, then what is the story behind this picture?

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While sorting boxes of old photos I came across this one – perhaps it was one of my Mum’s, I don’t know. Written on the back are the words “My grateful thanks to you both”. It is not signed. What was the story behind it? He may be a relative as I didn’t know many of my mother’s brothers as they live some distance away. It is a rather serene yet serious photo.

What do you think the story could be?