The Police Chief of Long Beach has confirmed that his department's policy is to detain photographers who do nothing more than take pictures in public places, and that he neither has, nor plans to implement, any guidelines for these detentions. He classes photography with other "suspicious activity" such as "attempts to acquire illegal or illicit biological agent (anthrax, ricin, Eboli, smallpox, etc.)" and "In possession, or utilizes, explosives (for illegal purposes)."
"If an officer sees someone taking pictures of something like a refinery," says McDonnell, "it is incumbent upon the officer to make contact with the individual." McDonnell went on to say that whether said contact becomes detainment depends on the circumstances the officer encounters. "
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And here's an example of a Police Officer being a Clown, assaulting a Camera Man for filming him:
Some bad Precedents on access to the Government's own footage:
http://www.thenewspaper.com/news/35/3557.asp
Rare cases when Credentials don't help, even if you are from a Television News Station: