Facial recognition technology in use at a Florida airport contains fatal flaws, according to research from the American Civil Liberties Union (ACLU).

The system failed to match volunteer employees (who had been entered into the database) in 503 out of 958 cases - or 53 per cent of the time, according to documents released to the ACLU.

Randall Marshall, legal director of the ACLU of Florida, said the test of facial recognition by security professionals has shown that "the technology is just not an effective way to increase our safety".

The group said that test subjects had to keep their heads perfectly still for the technology to stand any chance of working. The wearing of glasses complicated matters further.

"Motion of test subject head has a significant effect on the system ability to both capture and alarm on test subject," the report said. "Eyeglasses were problematic as glare from ambient light and tinted lenses diminished the system's effectiveness."

During lab tests, along with experiments at the Super Bowl and Palm Beach airport, similar results were discovered. "Facial recognition is a clunker that holds little promise to make us safer," said Marshall.

"It hardly takes a genius of disguise to trick this system. All a terrorist would have to do, it seems, is put on eyeglasses or turn his head a little to the side," he added.

The findings were based on the first four weeks of an eight-week trial of Visionics Argus facial recognition system at the Palm Beach, Florida security checkpoint. Around 5,000 passengers and employees a day were tested.