I'm really confused about this guy. Just recently, my friend uploaded a picture of me in this dress I had to wear for a public performance. He asked to see it and she let him. He commented on the photo with the adjective 'sexy'. My question is, what did he mean by that? Does he genuinely like me or something? Or did he say it as a joke as I noticed he was partially smiling/ giggling. I noticed he also likes to offer to help me out on things and annoys me by teasing me, e.g. He takes my things about jokingly blames me for things I haven't done.

Hi! I think to find out whether he likes you, you're going to have to watch his actions towards you for a little while longer but to me this does look like subtle flirting. He's using humour and small actions to get closer to you, and to also engage with you in either conversations or activities. As the for the picture and his comment, I wouldn't focus on that too much. From my experience, when guys comment 'sexy' on a girl's photo it can mean one of two things:

1) they're a f*ckboy
2) they say it in a joking way, but it's an indicator that they think it's a pretty picture

I say, keep on noting his actions and the things he says to you, and try and decipher whether he's flirting with you or not. I think it's quite early to say now, but I'm pretty sure he's subtly flirting.