I feel like the photography thing is also pretty straightforward.
Some people like to be photographed or at least don't mind being photographed.
Some people don't like to be photographed (or want a say over how they are photographed).
It's been argued in this thread that if you put on a costume you must want to be photographed, but that's pretty clearly not true. We have plenty of counterexamples. So if wearing a costume isn't implicit consent, how can we distinguish between the two groups of people? Well, the easiest solution is to simply ask for explicit consent before taking a picture. The people who are cool with it will say yes, the people who aren't will say no. Easy peasy.
Assuming you are an ordinary human being who gives moral weight to the preferences of other people, this is the best solution all around. You won't inadvertently take photos of people who would prefer you not to do so, they won't feel harassed, and all it requires is a modicum of effort in asking before doing.
Promoting this as a convention-wide standard of behavior would be a good starting point.