@bogo Everywhere, really.

Not sure how enforceable this is, the university grounds can probably be considered to be public, and Belgium allows photography in public.

Publishing those photos without consent is a different matter however.

@bogo idk I've always found that German law about blurring faces of strangers so bonkers. Must be the only country in the world that has one. And more generally, "you can look at it with your eyes but can't take pictures with a camera" just doesn't work in practice.
@bogo PyCon UK uses lanyard colour to indicate. Something like
Blue lanyard: photoes of me are fine
Red: do not photograph me
Green: event staff

@bogo a furry con I assist with has it in nonverbal communication form: ribbons!

They follow Kink Rules: positive an negative consent are easily given, can be revoked at any time (remove the ribbon) and can be signaled in group (look for crimson cameras, ask if they are okay excepting consent)