I accidentally sent the guy I'm hanging out with his own picture that I had  taken.
For what reason would you send him a picture of himself?
I didn't realize that I had sent it.
It's not a big mistake, so I'd chill. It's cool that you are hanging out together and have memories saved in pictures.
I guess, but ugh, fuck!
Don't be so down on yourself, you have nothing to be embarrassed about. It's fine to make a mistake and I'm sure this guy doesn't think badly about it at all.