The "Backscatter" machine to be used at Phoenix Sky Harbor International Airport in Arizona will enable screeners to detect non-metallic devices and objects as well as weapons on a person's body, authorities say.

But critics, including the American Civil Liberties Union, say the machine can display graphic images of nude bodies and its use will pave the way to widespread abuse of the images taken, with some possibly being posted or traded on the Internet.

Federal officials, however, have downplayed such concerns saying that screeners will be able to blur out a person's genitals and that the x-ray image will be erased from the screen once a passenger is cleared through the machine.

The Transportation Security Officer operating the system will also not be able to print, store or transmit the image and will be viewing the x-ray in an area not visible to the public.

Officials said "Backscatter" will be a voluntary option for passengers undergoing secondary screening and is an alternative to the physical pat down procedures currently conducted at security checkpoints.