Dopamine is a strange thing

Don't worry about it too much. I don't really know about your brain or your dopamine levels, but I like to focus on what I can feel and perceive myself. Dopamine is something you can measure in scientific experiment, but not feel. Moreover, it is a completely normal hormone which helps you survive.
It might have been risky behavior, but it clearly wasn't a relapse. Just seconding what you stated yourelf in that regard.
I had a look on some of these pictures myself. Weird stuff. Apparently these teens (mostly teens) don't care much for their online privacy. Google will become better at comparing images over the next years. When they apply for a job in a couple of years, the HR executive might find them over there, exposing themselves as being extremely self-conscious and insecure. Anyway, it's not my problem nor is it yours. But it still weirded me out.
There is definitely this vibe of 'look at me!', 'rate me!' and 'I am trying to look good on selfies' over there. It kind of feels like the other side of instagram model perfection to me. May be it is more similar than it seems on first glimpse. These insecure girls clearly feel the need to define themselves by their outer shell at last!
This is my first impression. Hope it helps you a little. It might be that it has a lot more in common with quasi-pornographic exhibitionism than it looks like on the surface. It is just as superficial to say the least. On instagram you have the winners, there are the losers. If they knew that true beauty shines from the inside, these girls wouldn't go there.
(And of course most of them don't even look that bad. What might make them 'ugly' is that they define their self-worth by outer appearance.)