Seems like a generally good idea to share this again.

“If stopped for photography, the right question to ask is, “am I free to go?” If the officer says no, then you are being detained, something that under the law an officer cannot do without reasonable suspicion that you have or are about to commit a crime or are in the process of doing so. Until you ask to leave, your being stopped is considered voluntary under the law and is legal.”

Know Your Rights: Photographers