Add a letter to a word, and you could change everything. Even if both words are extremely similar, they aren't interchangeable. Before you use one or the other, know the difference between person and persona.
Person simply means human being. It can be any man, woman or child. When there's more than one person, it becomes the plural people. It's a noun. Synonyms include body, character, individual and personage -- not persona, which is sometimes mixed up with person. They aren't the same.
A persona means essentially the same thing as image, but it can also mean a role that's being played (like by an actor). If you're greatly upset by something but pretending to be fine, you're presenting the persona of an untroubled person. Like person, this word is also a noun. A persona is a public image that one wears.
It's easy to use persona and person incorrectly; they're both nouns used to describe individuals in a story. If you're describing a specific character in the story, person is the correct choice. But if you're specially referring to some image that they're projecting, then you might describe something about that character's persona. It's easy to confuse the two because of the word personality, which can refer to a persona (a projected image or characteristic), but in a larger sense refers to a single person's inner workings as well as their projected image.