believe it is mostly common sense, but as stated varies by country and even site.
My gosh, almost every New England Calender, etc would have to be taken off the market. I treat it that if I am inan Urban setting, then the buildings, bridges and such are fair game.
And if you are in Time's square, well people are just there. Brooklyn Bridge, again, open public area.
but, zooming into people, it just gets complicated. I might take a picture for porfolio, but I would not market the picture without some
form of permission.
but, I know of pictures used in magazines that did not get permisssion.
There also famous places that copyright themselves, and state that while you can take a picture, don't try to sell it. The Eifel Tower in Paris is one of those places.
so,, seems again to be a hodge podge of rules that one has to have common sense..
and on NYC,, do visit, its a fantastic photo op.