One addendum; most states declare that photography is legal as long as the pic is being taken from publicly accessible property. This varies a bit state to state, but even standing on the sidewalk with a 500mm zoom taking shots through your open window is legal. Note the difficulty dealing with the whole paparazzi issue.

I ran into this issue several times as a police officer, and in each case had to explain to the aggrieved party that the law says it's ok, and that there's nothing I could do in the law to rectify the situation. This is, in fact, used by pedophiles on occassion, but there's harrassment statutes cops can use in such cases.

I completely concur with knowing one's rights. As a amateur photo hound on occassion I've been taken to task by over-eager security guards and had to explain that I was within my rights (there' s gorgeous abandoned old railway building in Portland that had a known over anxious Paul Blart type who would shout at you through the fence to show him your camera or he'd call the cops). I always delete a pic if asked; I'd rather defuse than be "right." Still, that guy who called the cops to deal with such a stupid issue? Nope. I'd have told him to pound sand and asked the cop (politely) for the statute. You'll always know if a cop is hedging by his response. If he gets bent about being questioned on the existence of a law in a non-violent suituation there's bigger problems afoot.

Being a citizen is sometimes standing your ground when you're right and it makes sense.