These days, it's not hard to see why police are wary of being filmed. In 1991, the Los Angeles Police Department (LAPD) beating of Rodney King was captured on video by a private citizen. It was shown repeatedly on television and caused a national uproar. As a result, four LAPD officers were put on trial, and when they were not convicted, riots broke out, leaving more than 50 people dead and thousands injured (two officers were later convicted on federal civil rights charges). (See TIME's special: "15 Years After Rodney King.")

More recently, a New York Police Department officer was thrown off the force — and convicted of filing a false report — because of a video of his actions at a bicycle rally in Times Square. The officer can plainly be seen going up to a man on a bike and shoving him to the ground. The officer claimed the cyclist was trying to collide with him, and in the past, it might have been hard to disprove the police account. But this time there was an amateur video of the encounter — which quickly became an Internet sensation, viewed more than 3 million times on YouTube alone. (Read about the hidden side of the NYPD.)

In the Graber case, the trooper also apparently had reason to want to keep his actions off the Internet. He cut Graber off in an unmarked vehicle, approached Graber in plain clothes and yelled while brandishing a gun before identifying himself as a trooper. (Comment on this story.)

Back when King was beaten, it was unusual for bystanders to have video cameras. But today, everyone is a moviemaker. Lots of people carry video cameras in their pockets, on iPhones, BlackBerrys and even their MP3 players. They also have an easy distribution system: the Internet. A video can get millions of viewers worldwide if it goes viral, bouncing from blog to blog, e-mail to e-mail, and Facebook friend to Facebook friend. (See photos from inside Facebook's headquarters.)

No wonder, then, that civil rights groups have embraced amateur videos. Last year, the NAACP announced an initiative in which it encouraged ordinary citizens to tape police misconduct with their cell phones and send the videos to the group's website, www.naacp.org.

Law enforcement is fighting back. In the case of Graber — a young husband and father who had never been arrested — the police searched his residence and seized computers. Graber spent 26 hours in jail even before facing the wiretapping charges that could conceivably put him away for 16 years. (It is hard to believe he will actually get anything like that, however. One point on his side: the Maryland attorney general's office recently gave its opinion that a court would likely find that the wiretap law does not apply to traffic stops.)

Last year, Sharron Tasha Ford was arrested in Florida for videotaping an encounter between the police and her son on a public sidewalk. She was never prosecuted, but in June, the American Civil Liberties Union (ACLU) of Florida sued the city of Boynton Beach on her behalf, claiming false arrest and violation of her First Amendment rights.

The legal argument prosecutors rely on in police video cases is thin. They say the audio aspect of the videos violates wiretap laws because, in some states, both parties to a conversation must consent to having a private conversation recorded. The hole in their argument is the word "private." A police officer arresting or questioning someone on a highway or street is not having a private conversation. He is engaging in a public act.

Even if these cases do not hold up in court, the police can do a lot of damage just by threatening to arrest and prosecute people. "We see a fair amount of intimidation — police saying, 'You can't do that. It's illegal,'" says Christopher Calabrese, a lawyer with the ACLU's Washington office. It discourages people from filming, he says, even when they have the right to film.

Ford was not deterred. According to her account, even when the police threatened her with arrest, she refused to turn off her video camera, telling her son not to worry because "it's all on video" and "let them be who they continue to be."

The police then grabbed her, she said, took her camera and drove her off to the police station for booking.

Most people are not so game for a fight with the police. They just stop filming. These are the cases no one finds out about, in which there is no arrest or prosecution, but the public's freedoms have nevertheless been eroded.

Ford was right to insist on her right to videotape police actions that occur in public, and others should too. If the police are doing their jobs properly, they should have nothing to worry about.

Cohen, a lawyer, is a former TIME writer and a former member of the New York Times editorial board