I don't have any photographs of me as a 13 year old and definitely none that are uploaded on to my computer! If I met my 13 year old self and this didn't cause a rift in both time and space it would be very tempting to try to offer some advice. The thing is I expect it would be hard to know where to start!
I think the main thing I would tell my past self would be not to worry so much about fitting in and being normal. I gave it ago once and ended up ignored and bored. I'd also try to explain that there's a reason you don't fit in with the people your hanging around with it's because they're not the people who you need to be friends with. Try to stick with the more artistic and bookish people they are your kind, they understand that you read to escape school not to be rude to anyone. (They also have the best computer games!)
Another piece of advice I'd give is that worrying about getting more confident won't help you get anymore confident it actually seems to have the opposite effect! I also used to get upset that no boys seemed to like me but this was really the last thing I should've been worrying about... it was just that I was a shy little thing with no clue that reading books hunched up in a corner wearing baggy clothes wasn't going to make me attractive. Seems obvious now but that took me a few years to figure out.
I'd also be tempted to give myself a couple of other pieces of advice like don't worry so much about school. Although might help to focus a bit more in class and stop reading till the early hours...
The last thing I'd do would be to tell myself that my parents are human and make mistakes just like everyone else. Another obvious point but it was something I didn't get as a screaming banshee of a teenager. It's also something I hope that my unborn son realises when he meets me, that we're all doing the best we can with the knowledge that we've acquired.
I wonder what advice my 39 year old self will have for me in another 13 years?