http://www.aclu.org/free-speech/know-your-rights-photographersKnow Your Rights: Photographers
Taking photographs of things that are plainly visible from public spaces is a constitutional right – and that includes federal buildings, transportation facilities, and police and other government officials carrying out their duties. Unfortunately, there is a widespread, continuing pattern of law enforcement officers ordering people to stop taking photographs from public places, and harassing, detaining and arresting those who fail to comply.
Your rights as a photographer:
When in public spaces where you are lawfully present you have the right to photograph anything that is in plain view. That includes pictures of federal buildings, transportation facilities, and police. Such photography is a form of public oversight over the government and is important in a free society.
When you are on private property, the property owner may set rules about the taking of photographs. If you disobey the property owner's rules, they can order you off their property (and have you arrested for trespassing if you do not comply).
Police officers may not generally confiscate or demand to view your photographs or video without a warrant. If you are arrested, the contents of your phone may be scrutinized by the police, although their constitutional power to do so remains unsettled. In addition, it is possible that courts may approve the seizure of a camera in some circumstances if police have a reasonable, good-faith belief that it contains evidence of a crime by someone other than the police themselves (it is unsettled whether they still need a warrant to view them).