I think you handled it wrong, but not in a bad way. If it were ME, I would have gone straight to the teacher/director/whoever and reported this. That's the kind of behavior I expect out of 12 year old girls (Tess? Are you there?), but not out of grown women.
Representing your school at a conference, and a public place, etc, ought to carry with it responsibility and a sense of maturity.
I don't blame you for being upset...honestly, if it was me, I would have carried it so much further. You don't know if they'd already emailed photos to someone else, if they really deleted them, etc...what they did was wrong on a lot of levels.
Maybe wrong for just gossiping about it at the bar, I don't know...not really gossip if you're passing along first hand knowledge, but it's a thin line. However, the consequences that may come from it are NOT your fault. Sounds like they've had it coming for awhile.