Interesting question .“A photo of me” only refers to a photo where you are depicted. “My photo” could also mean that, or it could mean you took the photo, or that you possess the photo (because you bought it or received it as a gift). For these last two meanings, you could also say “a photo of mine.” If the context doesn’t make it clear, you could say “a photo I took” to clarify that you were the photographer.