But Photojojo has compiled a helpful list of what you can and can't photograph in public. (Along with some legal resources and advice about what to do if you get stopped). Read their full post here
The Ten Legal Commandments of Photography
I. Anyone in a public place can take pictures of anything they want. Public places include parks, sidewalks, malls, etc. Malls? Yeah. Even though it’s technically private property, being open to the public makes it public space.
II. If you are on public property, you can take pictures of private property. If a building, for example, is visible from the sidewalk, it’s fair game.
III. If you are on private property and are asked not to take pictures, you are obligated to honor that request. This includes posted signs.
IV. Sensitive government buildings (military bases, nuclear facilities) can prohibit photography if it is deemed a threat to national security.
V. People can be photographed if they are in public (without their consent) unless they have secluded themselves and can expect a reasonable degree of privacy. Kids swimming in a fountain? Okay. Somebody entering their PIN at the ATM? Not okay.