I read this twice and I still don't know if you're male or female. In some ways, this matters.
Anyway, if your butt crack always shows and you drink too much at parties, you were practically begging for this. I don't think it's the end of the world that someone took the photos, but it's not ok to send them to the other 4 guys. It takes one person for something to go viral in 5 minutes. I don't get why you're not more upset about that.
Obviously, if any of these guys post it further, this is an enemy of yours you should never be around. TBH, though, all of this is creepy.
PS - I disagree with the answer saying to report this if you see it. Who would you report it to? It's not illegal to take a photo and post it. It's just dick behavior.