By Mark Ward
BBC News Online technology correspondent
Experts and official reports are casting doubt on plans to use iris scanning to improve security at national borders.
This week UK Home Secretary David Blunkett reportedly won the backing of his G8 counterparts to rapidly develop an iris-based biometric system as an extra check on the identity of international travellers.
But technical reports in the UK and US have expressed doubts about whether biometrics will be able to do what ministers hope they can.
Experts have also voiced reservations about large scale use of iris scanning which has yet to be tested on significant numbers of people.
This could be your passport in the future
Markus Kuhn, a lecturer in computer security at the University of Cambridge computer lab, said biometrics were gaining popularity because they were a relatively reliable way to verify someone's identity.
"There's a great amount of information in the iris that makes it possible to reduce the false accept/reject ratios to less than one in a million," he said.
"Biometrics are useful as confirmation of your claimed identity."
Certainly, said Mr Kuhn, biometrics were better at verifying identities than humans were when asked to match unfamiliar faces with small photographs in passports and other identity documents.
However, he added, their usefulness broke down when used to pick out wanted individuals, such as suspected terrorists, from the mass of people passing through a checkpoint.
With huge databases of biometric records it was likely that many people would be misidentified as being wanted or missed altogether, he said.
In February 2002 the US Department of Defence issued a report that found wide discrepancies between manufacturers' claims of successful biometric identification rates and those seen in the field.
The report found that iris recognition did better than most but one manufacturer's claim of a 0.5% false identification rate ballooned to 6% during the DOD tests.
With 13 million people currently on the FBI's watch list, any large scale biometric system could mean millions of people being detained when crossing borders.
Some biometrics are well established
Other studies of biometrics have also expressed doubts that the technology could be reliably used on a large scale.
A report issued by the US General Accounting Office in November 2002 said that the largest iris scanning system currently in use had only 30,000 records.
By contrast any system used to verify the identities of people travelling to and from the US, for example, would have to contain up to 240 million records. By comparison up to 90 million people travel through the UK every year.
The GAO warned that it was "unknown" how a system with many millions of records would perform.
It noted that any biometric system would do little to stem the numbers of illegal immigrants because most of them did not enter the US through recognised ports, and avoided all identity checks.
A report from the US National Institute of Standards and Technology issued last year said that, so far, not enough records yet existed for it to work out if the iris was a good enough guarantor of identity.
Professor Mike Fairhurst, a computer vision and biometrics expert from the Department of Electronics at the University of Kent, said getting large numbers of people to successfully use a biometric system could prove problematic.
"One of the problems is interaction between individuals and the system doing the checking," he said.
Tests of biometric systems by the UK's Communication Electronics Security Group have shown that people can take up to ten times as long to get through them than the existing passport checks.
"People have a natural resistance to different types of biometric measures," he said, "some cultures are not happy about touching surfaces touched by others and some people do not like lights being shone in their eyes."
China has already ruled out using iris scanning as an additional check for its new identity card because of public fears about the damage such scanning could do.
What would also have to be tightened up, said Professor Fairhurst, was the whole process of issuing travel documents or identity papers so only genuine people were enrolled.
He also said that the international standards for what constitutes a valid identity check by iris scanning had not yet been established.