[EricH]

Make 'em an offer: You'll stop taking pictures when (if) they start taking pictures and giving you access to them for promotional materials. Evil eyes and sarcasm mean two pictures get taken instead of one--which diminishes the odds of any one picture ending up in public, but increases the odds of that one picture having someone looking really dumb.

Either you'll suddenly get a bunch of photographers in-shop, or you'll get a bunch of pictures for an end of year "Faces of the Students" video...