Delta Air Lines has announced it is starting to use biometric technology to board passengers on flights from Detroit Metropolitan Airport to Tokyo.Detroit is the third airport where the technology is being used for boarding Delta flights, following New York/JFK and Atlanta's Hartsfield-Jackson International Airport.Airline officials said biometric screening will be added to more flights and destinations in the next few months. Beijing, Seoul, and Shanghai are among the other international cities with nonstop Delta flights out of Detroit.Rather than showing a boarding pass, travellers merely step up to a camera that scans their face to verify identity. In addition to boarding, Delta has deployed biometric technology for baggage drops and for entry into airport lounges.”From unlocking our phones to entering the workplace, more and more people have the option to use biometrics as a form of identity verification for daily activities,” said Gil West, Delta's chief operating officer.Boarding via biometric identification is optional for passengers, who may still present a boarding pass at the gate if they prefer, according to Delta.