This may not apply to every state.  However I am reading an article in which people caught taping (audio/video) a cop get arrested.  
http://able2know.org/topic/165784-1
"Police Officers Don't Check Their Civil Rights at the Station House Door"
Three law enforcement officials defend the arrest of citizens who record on-duty cops.
Radley Balko | August 9, 2010
The debate over whether citizens should be permitted to record on-duty  police officers intensified this summer. High profile incidents in  Maryland, Illinois, Florida, Ohio, and elsewhere spurred coverage of the  issue from national media outlets ranging from the Associated Press to  Time to NPR. Outside the law enforcement community, a consensus seems to  be emerging that it’s bad policy to arrest people who photograph or  record police officers on the job. The Washington Post, USA Today, the  Washington Examiner, The Washington Times, and Instapundit’s Glenn  Reynolds, writing in Popular Mechanics, all weighed in on the side that  citizen photography and videography can be an important check to keep  police officers accountable and transparent.
But so far, there’s been little activity in state legislatures to  prevent these arrests. That’s likely because any policy that makes  recording cops an explicitly legal endeavor is likely to encounter  strong opposition from law enforcement organizations. So what’s the  justification for bringing and supporting charges against people who  record or photograph cops? I recently spoke to three law enforcement  officials about it. Two are prosecutors currently pursuing felony  charges against citizens who made audio recordings of on-duty cops. The  third is the executive director of the Fraternal Order of Police,  America’s largest police union.
But so far, there’s been little activity in state legislatures to  prevent these arrests. That’s likely because any policy that makes  recording cops an explicitly legal endeavor is likely to encounter  strong opposition from law enforcement organizations. So what’s the  justification for bringing and supporting charges against people who  record or photograph cops? I recently spoke to three law enforcement  officials about it. Two are prosecutors currently pursuing felony  charges against citizens who made audio recordings of on-duty cops. The  third is the executive director of the Fraternal Order of Police,  America’s largest police union.
Joseph Cassilly is the Harford County, Maryland state’s attorney. He’s  currently pursuing felony charges against Anthony Graber, who was  arrested last April for recording a police officer during a traffic  stop. Maryland is one of 12 states that require all parties to a  conversation to give consent before the conversation can legally be  recorded. But like nine of those 12 states, Maryland also requires that  for the recording to be illegal, the offended party must have had an  expectation that the conversation would be private. To bring charges  against Graber, Cassilly would not only need to believe that on-duty  police officers have privacy rights, but in the Graber case in  particular, that a cop who had drawn his gun and was yelling at a  motorist on the side of a busy highway would, also, have good reason to  believe the entire encounter was private. This seems all the more absurd  given that motorists in such a situation clearly don’t have any  reasonable privacy expectation. Anything they say during such a traffic  stop is admissible in court.
"The officer having his gun drawn or being on a public roadway has  nothing to do with it," Cassilly says. "Neither does the fact that what  Mr. Graber said during the stop could be used in court. That’s not the  test. The test is whether police officers can expect some of the  conversations they have while on the job to remain private and not be  recorded and replayed for the world to hear."
Last February, University of Maryland student Jack McKenna was beaten by  riot police after a basketball game. Cell phone videos of the beating  contradicted police reports, and resulted in the charges against McKenna  being dropped and in the suspension of several police officers. Would  Cassilly have charged those cell phone videographers with felonies if  their recordings picked up audio? After all, it's the audio portion of a  video that triggers state wiretapping laws.
"In College Park you had lots of people around, you had people screaming  and shouting. The officers in that case had no reason to think the  situation was private," he says.
Cassilly’s interpretation of the law is awfully vague. How is your  average Marylander supposed to know if taking video of what he thinks  may be police abuse is protected speech or if it's a felony punishable  by possible prison time?
"I don’t have any hard and fast rule I can give you," Cassilly says. "It  depends on the circumstances, and if the officer in those circumstances  had good reason to think he wouldn’t be recorded. Should a domestic  violence victim have a camera shoved in her face and have her privacy  violated because someone is following a police officer around with a  camera? What if he’s collecting information from witnesses at a crime  scene? I’m saying that not everything a police officer does on the job  should be for public consumption."
Generally, Casilly says, police actions in front of large crowds of  people can probably be recorded. But citizen recorders put themselves in  legal jeopardy when there are fewer people around, and an officer is  more likely to think his conversations are private. But this seems to  negate the use of citizen recording when it would be most important as a  tool to hold misbehaving police officers accountable. Misconduct in  front of large groups of people is obviously more likely to produce lots  of witnesses to challenge the police narrative of the event.
What if a police officer is harassing or intimidating someone in close  range, such as during a traffic stop, or on an unpopulated street at  night? Would it be a felony to record those interactions? What if the  recording captures unquestionable lawbreaking on the part of the  officer, such as a threat or a shakedown? "I’m not going to respond to  any hypothetical scenarios," Cassilly says. "It just depends on the  circumstances."
Last month, the office of Maryland Attorney General Doug Gansler issued  an advisory opinion that would seem to be at odds with Cassily’s  interpretation of state law. Gansler's office found that "it’s unlikely  that most interactions with police could be considered private, as some  law enforcement agencies have interpreted the state's wiretapping act."  But that opinion isn’t legally binding, and may not affect Anthony  Graber’s case. In fact, when I spoke with Cassilly (we talked before  Gansler’s opinion), I asked him about a 2000 Maryland AG’s opinion  stating that motorists have no privacy expectations during a traffic  stop. Cassilly replied, "Those opinions are just the attorney general  paying some lawyers to tell him what he already thinks. I don’t have to  agree with it."
Unlike Maryland, the law in Illnios is much clearer. It is illegal to  record anyone in public without their consent. The state has no  stipulation about privacy expectations. It once did, but the legislature  removed that provision in 1994. That amendment was actually a direct  response to a state supreme court decision throwing out the conviction  of a man who recorded two cops from the back of a police cruiser. In  Illinios, felony eavesdropping is in the same class of crimes as sexual  assault. It’s punishable by 4 to 15 years in prison.
Crawford County State’s Attorney Tom Wiseman is currently bringing five  felony charges against Michael Allison, a 41-year-old construction  worker who recorded police officers and other public officials he  thought were harassing him. (I'm writing a feature about Allison's case  for a forthcoming issue of Reason). Allison was fighting a zoning  ordinance forbidding the storage of unregistered or inoperable vehicles  on private property. Allison thought he was being unjustly targeted by  local authorities and was planning a civil rights lawsuit, so he began  recording his conversations with local law enforcement. He faces up to  75 years in prison for the recordings.
I first asked Wiseman if he thinks Michael Allison should spend the rest  of his life in prison for making audio recordings of on-duty public  officials. "My job isn’t to write the laws. My job is just to enforce  them," Wiseman says. Wiseman does have discretion over whom he charges.  But he says Allison committed a felony, and that it wouldn’t be proper  for a prosecutor to overlook a felony. But Allison thought the police  were harassing him. Given the deference law enforcement officials get  from courts and prosecutors, how can a citizen who feels he’s being  harassed or treated unfairly by law enforcement protect himself?
"The only person doing any harassing here is Mr. Allison, who was  harassing our public officials with his tape recorder," Wiseman says.  "They may have problems with some bad police officers in some of your  urban areas. But we don’t have those problems around here. All of our  cops around here are good cops. This is a small town. Everyone knows  everyone. If we had a bad police officer here, we’d know about it, I’d  know about it, and he’d be out. There’s just no reason for anyone to  feel they need to record police officers in Crawford County."