US Government Issues Bulletin to Police Explaining Photographers' Rights
The New York Times reported this week that a bulletin sent out last August should be clearing up this problem. Among other things, it explains the rights of photographers to take pictures of public buildings from public spaces.
It also explains that officers with reason to stop a photographer " should not seize the camera or its contents." They shouldn't ask for pictures to be deleted either, as " this constitutes a seizure or detention."
You can read more on this and even get a copy of the full bulletin from the New York Times.
