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 and continuing pattern of law enforcement officers ordering people to stop taking photographs from public places. They often quickly resort to harassing, detaining, arresting, and even fabricating false charges against those who fail to comply. This video taken in 2012 is a shining example.
KNOW YOUR RIGHTS AS A PHOTOGRAPHER: American Civil Liberties Union (ACLU)