This was a short story, told in the third person. Written in English. I first read it in a library book, sometime during the 1980s, probably no later than 1986. (I lived in Indiana at the time.) I'm pretty sure it was in an anthology of stories by various authors. No telling how old the story already was when I read it; nor how old that particular book was. I've never run across the story in any other volume, which makes me pretty sure it wasn't by such big names as Isaac Asimov, Arthur C. Clarke, Roger Zelazny, etc. The plot was very simple; I'm tempted to say "downright corny by modern standards." (But I restrain myself.)
The protagonist is a bachelor who is a trained photographer. He does a lot of restoration work on faded old photographs, decades old. A typical client might say, "This is all I have left to remember Grandma and Grandpa by," and then the protagonist would try to make it look more crisp. The author gave some technical details about how this was done; enough to make me think the author actually knew something about the chemicals and tools of pre-digital photography. (Not that I would have known if the author flubbed some of the details.)
Gradually, the protagonist begins to have moments when he seems to be "living within the photograph" -- i.e. standing off to one side of the scene in question, seeing the relevant people in full color, hearing them talk to each other, feeling the wind on his face, etc. The first time this happens, it wears off pretty quickly. He is alone in his studio, with no witnesses, and is keenly aware of the possibility that he simply dreamed or hallucinated the entire thing.
Nonetheless, he decides to let this glimpse into the past inspire him. In other words, he uses his vivid memories of that brief visit to guide his restoration work on certain details of clothing and facial features and so forth, in the photograph which triggered the event. Afterwards, the current client is satisfied with the results. (Of course, the photographer doesn't say a word about having slipped back in time to get a good look at Grandma and Grandpa in their prime; the client might not understand.)
Eventually, while staring at another old photograph, the protagonist ends up at some sort of "church picnic" or similarly wholesome social event, in a certain small town in the USA, around the early years of the 20th Century, and begins to strike up a conversation with a sweet and charming young lady. (The protagonist is a lonely man with no wife or girlfriend in the "modern world," you understand.)
In the end, he deliberately goes "back into" that photograph for another visit -- or perhaps he plunged into another photo of some of the same people when he encounters it later; I'm not sure. It is at least implied, if not stated outright, that he can and will stay in that past era permanently, supporting himself with his detailed knowledge of photographic techniques, and (presumably) will marry the charming young lady after a lengthy courtship process.
Does anyone recognize it from the description?
P.S. As I look back at what I just typed, it strikes me that when I summarize the plot this way, it ends up sounding like the sort of unabashedly nostalgic thing that Ray Bradbury sometimes wrote -- but I'm almost certain it wasn't one of his. For one thing, I don't remember ever running across it in any of the collections of Bradbury's short stories which I've enjoyed at various times since then. And I don't think the writing style was reminiscent of Bradbury's. Plus the fact that I'd probably have remembered his name was attached to it; I believe I'd already read The Martian Chronicles and some of his other works before I ever read this story about a photographer.