Gizmodo and Reason have posts here about people who have faced criminal charges for recording on-duty police officers. One case involves an artist selling his work on a Chicago street, who was deliberately trying to get arrested so he could challenge the law in court. A judge has refused to dismiss a felony charge against him for wiretapping.
The legal justification for arresting the "shooter" rests on existing wiretapping or eavesdropping laws, with statutes against obstructing law enforcement sometimes cited.
Illinois, Massachusetts, and Maryland are among the 12 states in which all parties must consent for a recording to be legal unless, as with TV news crews, it is obvious to all that recording is underway. Since the police do not consent, the camera-wielder can be arrested.
Reason points to the case of Michael Hyde, a man who secretly recorded a traffic stop in Massachusetts. His conviction on wiretapping was upheld by courts, who pointed out that secret recordings were banned by law. The Boston Globe had a piece earlier this year about others who were arrested for recording police encounters.
I'm still trying to find a police perspective on this. I can't imagine anyone wants to have everything they do at work scrutinized -- and from their perspective, taken out of context. But there have also been cases of police abuse that were caught only because someone had a camera handy.
Hat Tip: Saw this via Fark!