If you are looking at a photo, this means you see the action in the photo at this moment. "What are they doing in the photo?" It doesn't matter how long ago the photo was taken. You see the action in the present moment, and that's how you describe it.

Both are OK, but "are" is better than "were". When describing a creative production (a book, a movie, a painting, o a photograph), we usually use present tense, since the production still exists. For example, we would usually say, "In this movie, a man *fights* a dinosaur." If the main reason we're talking is to tell a story instead of describing the book or movie that contains the story, we will use past tense instead of present. This usually happens if the description is longer than two sentences or so. For Example: "I saw a movie yesterday. It was about a man who fought a dinosaur. He punched it, and it clawed at him. Then, some aliens came and killed both the man and the dinosaur."

Are you asking what the people are doing in the photo (as the photo was taken)? Or are you asking what the people do, as in what they do for work? I will assume, for now, that you mean the former; so, if you are shown a photo of people and you are asking what they are doing as the photo was taken you could say: "What are they doing in this photo" or "What were they doing in this photo". "What are they doing" and "What were they doing" would also suffice since it can be assumed that you are talking about the photo. Let me know if this helps or not. Peace.