(NEW YORK, NY) - An X-ray scanner that can see through clothing is setting off alarms for those who say using the machine on air travelers constitutes an invasion of privacy.

The U.S. Customs Service has been using the BodySearch device at John F. Kennedy International Airport and five other major airports around the country to search for contraband for most of this year. Plans are to have it installed at all of the country's major airports by June of next year.

The machine uses low doses of X-rays to scan a traveler, displaying an image of the person's body on a screen. It looks like an outline filled in with white chalk, but doesn't show physical details like a photograph would.

The display does show anything that is being carried either in a person's clothing or on the body, such as weapons or packages of illegal drugs.

Customs Commissioner Raymond Kelley said Wednesday that anyone who is subjected to a search at an airport where the device is in place would have an option of undergoing a physical pat-down instead of being scanned by the machine.

"People object to being physically touched," he said. "In response to that we brought in the scanners."

Customs is facing numerous lawsuits from people alleging they were singled out for body searches because of their race or sex. The allegations first were reported by The Associated Press last year.

But some say the X-rays are more invasive than a pat-down, since the scan shows the outline of a traveler's naked body.

In testimony to an international conference on aviation safety, Gregory T. Nojeim, legislative counsel for the American Civil Liberties Union, said the scanner can show private parts with clarity and that portions of the display could be enlarged by the viewer.

"If there is ever a place where a person has a reasonable expectation of privacy, it is under their clothing," he said in his testimony.

But Robert Peters, vice president of American Science and Engineering of Billerica, Mass., which makes the machines, said concerns about the images were exaggerated, noting that the display doesn't show specifics such as scars, birthmarks, or even muscle definition.

"It's not like you're getting a photograph of a naked person," he said.