From a really rather marvellous essay on billjayonphotography.com, comes this list of rules for amateur photographers, written in The Amateur Photographer some time around the turn of the 20th Century. Number six is alarmingly prescient, given the current difficulties in photographing in public.
1) Never photograph a man in such circumstances as you yourself would not like to be
2) Certain classes should be tabooed:
a) Public personages travelling incognito.
b) People labouring under physical deformities.
c) People suffering from temporary accidents, e. g., the occupants of a Channel
steamer after a stormy passage.
d) In general, people who implicitly or explicitly express a dislike to be photographed.
3) Never use an expedient to prevent a person knowing he was being photographed,
when, if he did know, he would probably resent it.
4) Never let the fact that the victim “didn’t know” excuse a violation of good taste.
5) Never use a camera as a medium for “a thundering good
6) Finally, remember that though you may escape without penalty, your misdoings will
be held against the brotherhood in general.