My mam too has recently started thinking people in photos are actually in the room. She will talk to them, and whisper if she doesn't want them to know what she is saying. She also started to think the same of people in the tv. Watching a program with babies on a couple of months ago, she was cooing at them, and said ' ooh they like it when I coo at them don't they, they are smiling at me'. She also tickles people in photos. But the photos do make her happy, so I just go along with it.
The ideas from other people sound good, using non perishable foods. As for moving the photo, I think it would depend on whether the photo causes distress, or it is becoming a problem in some way, if she is not eating due to giving all her food away etc. Best of luck with it.