What does it mean if a girl gives you a picture of her for your birthday?

It means she wants you to think that she is beautiful. If you like her, tell her how you feel because its obvious she likes you, if not you need to set her straight and tell her that you don't llike her

it means she likes you, and she wants you to like her back, or atleast think of her

It means that she wants you to think of her. It's obvious that she likes you and wants to know if you feel the same about her. If you do, don't be shy; tell her how you feel. If you don't have any special feelings for her, you need to set the record straight by telling her so. Let her down easy so you don't end up hurting her too much.

(P.S. Either that or she couldn't find anything else to give you on your birthday.)

it either means she's very self-centered or she's totally hinting she likes you

another :

it means she totally likes you! and she wants you to remember her. if you like her back, now is the time to tell her.