I was never sure about this either but every so often i do the sticker on the face thing with Thea. She's been taking it off her own face and not trying to take it off the mirror since she was about 11 months so im assuming she knows its her in the mirror. I keep trying it every so often just to make sure its not a fluke lol.
She also knows when she is looking at photo of herself because she tells you its her, she say "awwww ta-ya " and then points to herself. Thats a recent thing though. She's just over 14 months now.
I think all babies grasp things are different times, they are all individuals.