No entry for zombies (Image: c.AMC/Everett/Rex Features)

IF AN invading zombie army is staggering towards your front door, don’t worry: a fingerprint-activated door lock could save your bacon. That’s because one group of researchers has worked out how a biometric scanner can keep the undead at bay.

OK, so they weren’t specifically trying to stop zombies, but there is genuine concern about dead flesh being used to spoof fingerprint scanners. Severed fingers and even fingers cut from corpses can be used to give the bad guys entry to secure facilities, to steal cars or log on to computers.

It sounds outlandish, but the first reported case was in March 2005, when thieves stole a biometrics-activated Mercedes in Kuala Lumpur, Malaysia. Initially they took the owner with them so he could start the car, but they soon tired of his presence – and hacked off his digit before dumping him at the roadside.


To combat such bloody skulduggery, researchers at Dermalog Identification Systems in Hamburg, Germany, have developed a way for a fingerprint scanner to differentiate between live and dead tissue.

The trick is based on the way living tissue “blanches” – or changes colour – when blood is squeezed out of capillaries, as a fingertip is pressed against a surface, for example.

Clarissa Hengfoss and her colleagues at Dermalog found that living fingers absorbed LED light at 550 nanometres on first contact and then at 1450 nanometres as the skin blanched when fully contacting the sensor (Forensic Science International, DOI: 10.1016/j.forsciint.2011.05.014). In contrast, fingers from three cadavers showed no such change.

“The spectra for light and strong contact pressure were more or less identical for fingers from dead bodies,” the Dermalog researchers say. They hope their technique will find its way into future scanners to “serve as a criterion for authentication of a living finger”.

“A living finger can be distinguished from a dead one by the way it blanches when pressure is applied”

Using a severed finger is not the only way to cheat a biometric test: fake fingerprints can be created by imprinting copies in rubbery gels or silicone plastic, says Marcela Espinoza of the Institute of Police Science in Lausanne, Switzerland.

So Espinoza is working to identify the factors that give away a fake based on the way fingerprint whorls are distorted by the different kinds of moulds used to cast them. Gel prints are made either from a direct impression of a fingerprint or by using a photo of a print to make a mould. Both methods can produce telltale spacings between ridges and furrows that mark the print as a counterfeit. “We are developing an algorithm that detects these forgeries,” Espinoza told New Scientist.

The work both teams are doing is topical, says Tony Mansfield, a biometrics specialist at the UK’s National Physical Laboratory in London. “The International Standards Organisation is drafting standards for secure biometrics – and liveness and forgery detection are among the anti-spoofing measures. This work will probably feed into their thinking.”