A series of exposes and tests have exposed the shortcomings of systems that use face recognition, iris scanning and fingerprints to improve security.

Experts have found that the systems can be fooled using very simple techniques.

An American civil liberties group has condemned plans to use biometric systems to protect some US landmarks from attack.

Poor performance

Following the 11 September attacks many organisations have been looking for better ways to verify identities or even to try and pick out known terrorists or criminals from crowds.

Before now biometric systems had been seen as a good candidate for vetting people, but recent trials and tests are casting doubt on their effectiveness.

A report into the use of a Visionics face scanning system tested for eight weeks at Palm Beach airport in Florida only managed to correctly identify people 47% of the time.

Some landmarks are now using biometrics to scan visitors

The system is intended to scan crowds and pick out the faces of people it knows.

The airport tested the system by asking it to pick out the faces of 15 employees who were passing through the terminal.

The system struggled to identify people if they were wearing spectacles, if the lighting was wrong or if they moved their heads too much.

The poor performance has convinced the airport's authorities to abandon plans to use the face scanning system for security.

Despite the critical report the Visionics system is now being trialled at some American landmarks such as the Statue of Liberty.

"The facts show that under real-world conditions, Osama Bin Laden himself could easily evade a face recognition system." said Barry Steinhardt, director of the ACLU's Technology and Liberty Program, in a statement condemning the trials.

Fooling with photos

German technology magazine c't had more bad news for sellers of biometric systems when it carried out tests on 11 gadgets that used face and fingerprint recognition as a security measure.

The journalists found that they could fool some facial recognition systems by holding up a laptop showing a video of someone's face to the camera or even with a still image of a face.

They found it was possible to fool some fingerprint sensors by simply breathing on the prints left on sensors or by resting a small bag of water on the sensor.

Last month engineering professor Tsutomu Matsumoto revealed how he and his colleagues had managed to fool 11 commercially available fingerprint sensors using household ingredients.

By making false fingers out of moulds made from real fingers and digitally enhanced images, Professor Matsumoto managed to fool the fingerprint sensors 80% of the time.

The series of experiments led security researchers to declare that fingerprint sensors were too insecure to use seriously.

In defence, biometric experts say that the systems are good when ensuring small populations of people are who they claim to be, such as employees entering an office block.

But they fare badly when asked to pluck identities out of a crowd.