This is actually the opposite of the question asked, but nowadays it is
possible to take a picture almost anywhere without anyone noticing.
There are places where you are forbidden to take photos (eg. with anything
over a 200mm lens at the Australian Open tennis), but it is simple to
break the rule. I have a small camera with a 5-100mm lens. As it is not
35mm, this is actually a 28 - 560 mm equivalent.
It is also forbidden to take videos at all - but almost any camera today
will take video.
And if you have a 20 megapixel camera, you can take a photo and blow up
that little bit in the middle.
And you don't have to put a camera up to your eye to take a picture.

--
Edward McArdle