[rexarex]

Did these participants sign a release on the photos or was this snapped without consent?

[swores]

I can't speak to this one specifically, but most events have agreeing to be photographed as a default condition for attending. It's pretty much 101 for anyone with any experiencing running an event (unless it's an event where there's some specific reason to not want any photos of).

[murermader]

Normally, when you take part in a Hackathon, you agree to being photographed while at the venue.