> If I attend a conference I have the right to stay anonymous.

Sadly, legally you have no such right. You are in a public space, and anyone can take your picture freely and do pretty much what they want with it. Our society doesn't even have coherent social norms about reasonable rights to privacy in public spaces, much less law.

I agree that it would be reasonable to expect some level of anonymity, though. Hopefully some day it will be.