UK's largest airport, London Heathrow, will install facial recognition scanners by September for international and domestic passengers to prevent illegal immigration in the country. The scanners will go in terminals one and five, where international and domestic passengers commingle, said Mary Kearney, senior media relations manager for BAA, which operates Heathrow.

The facial recognition scanners will ensure that ticketed passengers board their correct flight. It will prevent, for example, a passenger who arrives from Miami from trying to use a domestic ticket obtained from someone else in the departure lounge and then flying to Glasgow.

Since domestic flights do not have immigration counters, it would be possible with the departure lounge arrangement in those terminals for a passenger from Miami to avoid immigration.The departure lounge allows international and domestic passengers to be together so that the domestic passengers have access to the lounge facilities, according to BAA.

A passenger's face will be scanned after they've obtained their boarding pass and just before security. Before the person boards their flight, their face will be scanned again once they've left the departure lounge.

The facial recognition technology comes from Aurora Computer Services, a U.K. based company. It's called the Aurora Image Recognition (AIR) system and uses a camera with an infrared flash, which the company says can function in either bright or low light. It can identity a person from about three feet away. The camera verifies a person's identity using biometric details, identifying a person in 4.7 seconds, a time that includes properly positioning a passenger, according to Aurora.

The AIR is used in combination with the Passenger Authentication Scanning System (PASS), which is made by the company Atkins. PASS links a person's travel documents with their photograph and has been used in other parts of Heathrow since 2008.