With very constrained exceptions, in most jurisdictions of the United States, it's entirely legal to take a photograph of an individual in a public place and post it to the Internet without their permission.
However, normally this has to be made explicit (through signs, or the like) - it's assumed it is allowed unless otherwise stated.
I wonder if going forward conferences will consider banning photography in future, for better or for worse.
The photograph doesn't seem to really be the issue, just an obvious thing that Adria did "wrong" for people to seize upon.
It seems like the exact same situation could occur if she had simply reported them through their names rather than through photography.