Grainy cell phone images are often used against cops accused of using excessive violence. Now, officers are being armed with their own cameras.

The so-called head cameras are the latest technology to come from TASER International, Inc., makers of the stun guns popular with law enforcement.

"It's like the helmet cam you've seen on X Games," said San Jose police officer William Pender, who demonstrated the camera on a recent afternoon.

Eighteen of San Jose's more than 1,300 sworn officers have been trained to use the AXON head cameras as part of a free trial. Other departments are expected to be added to the program.

Experts say the head cameras could help catch officers behaving badly and clear those who are falsely accused so long as they are accompanied by police department policies requiring they be switched on during each encounter and not as an officer chooses.

"I think it will also make the officers very aware that their behavior is being documented, which could cut down on possible police excesses," said Sam Walker, professor emeritus of criminal justice at the University of Nebraska, Omaha.

The device resembles a Bluetooth earpiece and is attached by a band that runs around the back of the officer's head.

It can be connected to an on-and-off button on the officer's chest, and from there to a video screen on a holster. In San Jose, officers are required to switch on the cameras for even routine investigations, such as vehicle stops.

At the end of an officer's shift, the device is placed in a docking station, where it recharges and its content is downloaded and stored on a secure server offsite. A three-year contract for the system for one officer that includes software and video storage costs $5,700, said Tom Smith, chairman and founder of TASER.

"People have been using (this technology) against us for years, unfortunately only for the bad stuff," Pender said. "So it'd be nice to show our view and our side of what's going on."

San Jose police came under fire recently after cell phone video surfaced showing officers striking and using a Taser on an unarmed Vietnamese student, Phuong Ho, during an arrest in September. Police are investigating the incident, but an attorney for Officer Kenneth Siegel, who is seen repeatedly hitting Pho with his baton, says the suspect was combative and resisting arrest.

Police officials say the pilot program, which has been in the works for more than a year, is not a response to the incident.

The device will capture the context for an officer's response to a suspect, said Jermaine Thomas, a spokesman for the San Jose police.

Additionally, the video and audio captured by the device cannot be tampered with, TASER officials say.

The AXON camera already has proven its worth in the only other police department that has tested it so far.

Prosecutors cleared a Fort Smith, Ark. officer of any wrongdoing in the fatal shooting Nov. 11 of a man suspected of threatening his wife with a handgun.

Officer Brandon Davis was wearing an AXON camera when he confronted Eric Wayne Berry. In the video released to the media, the officer's gun is drawn as he repeatedly tells Berry, who authorities say was armed, to drop his weapon before opening fire.

While noting there were several witnesses to the incident, Sebastian County prosecutor Dan Shue said in a letter clearing Davis that the video and audio enabled him to "observe what happened with complete objectivity."

"Any evidence that we got about what had taken place is what we're looking for," said Joseph Self, chief deputy prosecutor in Shue's office. "We're in the search for the truth here."

Skyler Porras, director of the American Civil Liberties Union's San Jose office, argued that departments should not only have policies about when to use the cameras but also should allow independent reviews of the video to ensure officers are following the rules.

"We need to know, 'Are officers turning video cameras on at the very beginning of an engagement with a resident? Which officers have a 15 percent failure rate in turning it on?" she said. "If they are used appropriately and with proper protocols in place, they could be useful."