The idea of gait recognition has been around for a long time. In G.K. Chesterton’s short story The Queer Feet, Father Brown prevents a crime by “merely by listening to a few footsteps in a passage.” Gait analysis has been widely deployed in professional sports and medicine, enabling sports stars to improve their golf swing, running stance or cycling position and helping in the design of prosthetic limbs for example.

As a means of identifying someone at a distance, without any need to inconvenience the people being analysed, it would appear to be a useful proposition. It is important to note, however, that identifying someone in a crowded city square and verifying that someone is one of 200 people who have walked down a colourful corridor with clear contrast under carefully controlled laboratory conditions, are two entirely different problems.

Technically speaking, checking the gait of one person, in a psychedelic corridor with perfect lighting conditions, to find a match in a database of 200 recorded gaits, is relatively straightforward.

Detecting individual gaits in a dynamic, crowded city square, under less than ideal lighting conditions and pinpointing a baddie by attempting to match those (potentially) millions of readings against a database of millions of recorded gaits, is a much more difficult problem.

And we haven’t even thought about how we would get accurate measurements of millions of people’s (or indeed the baddie’s) walking styles on our benchmark database in the first place yet. Then if the baddie puts a stone in his shoe to change his walk to deliberately fool the software, as Dallas did with his funny walk on the first programme in the Bang Goes The Theory series, it becomes even more difficult.

From a security perspective, the notion that mass surveillance with advanced technology will magically detect the baddie, turns out to be fundamentally flawed. (It should be noted that mass surveillance is widely and wrongly promoted as an effective anti-terror tool but it is not advocated by the team at Southampton.)

Because terrorists are relatively rare, finding one is a needle in a haystack problem. You don’t make it easier to find the terrorist by throwing more hay (say the biometric data of millions of innocent people) on your data haystack. The technology doesn’t simply home in on the criminal as it does in Hollywood movies.

The police and security services end up spending so much time dealing with innocent people and false leads that their limited resources get swamped.

If each of the UK’s population of around 60 million were monitored once a day and our system was 99% accurate (e.g. flags 1 in a 100 innocents as terrorists and detects 99 out of every 100 terrorists), the police will have to process 600,000 false leads per day.

Given those of us who traverse public places are monitored multiple times a day you can see how that could quickly become unmanageable. It’s also unacceptable from a social, legal and economic point of view.

So it is probable that the use of gait recognition and other biometrics will prove to be more useful for small scale authentication - e.g. employee access to the workplace, rather than large scale surveillance e.g. picking a terrorist out of a crowd.

On small-scale authentication

Technically speaking authentication or verification is an easier thing to do than identification. Authentication (assuming we’re not trying to do it remotely) with biometrics merely asks whether a biometric belongs to the person presenting themselves for authentication. It compares their proffered biometric with the one on file under their name and determines whether there is a match.

Identification is much harder to do and is what security systems at airports or busy shopping areas or sports stadiums attempt to do – measure the biometrics of everyone passing through and attempt to check whether there is a match with a large (and not necessarily particularly reliable) database of biometrics.

The difference appears pedantic but is very important. In the authentication case one biometric is checked against one specific biometric on the database. In the identification case, millions of biometrics are checked against millions (potentially) of biometrics on the database.

Even with highly reliable technologies – say 99.9% accurate and none of the modern systems approach that yet – these millions of checks searching for matching pairs generate huge numbers of false positives (innocents flagged as malcontents) and dangerous levels of false negatives (real bad guys flagged as innocents and it only takes one to get through to cause serious security problems).

The police and security services then spend so much time, energy and resources dealing with innocent people they don’t have the time to deal with the real criminals.

Find out more

Floyd Rudmin, Professor of Social & Community Psychology at the University of Tromsø in Norway, explains why, statistically speaking, mass surveillance cannot work in this article:
The Politics of Paranoia and Intimidation: Why does the NSA engage in mass surveillance of Americans when it's statistically impossible for such spying to detect terrorists?
Counterpunch magazine, May 24, 2006

For those interested in the use of biometrics and security more generally I’d recommend:
Beyond Fear: Thinking Sensibly About Security in an Uncertain World
Bruce Schneier, Springer-Verlag New York Inc

Freedom to Tinker blog - hosted by Princeton's Center for Information Technology Policy.

Jerry Fishenden Blog - New Technology Observations from a UK Perspective.

UK High Court Judge, Hon Sir Jack Beatson explains the legal issues with the use of biometrics in crime detection in Forensic Science and Human Rights: The Challenges [pdf], his valedictory address as President of the British Academy of Forensic Science, 16 June 2009.

Nuffield Council on Bioethics report, The forensic use of bioinformation: ethical issues [pdf], published in September 2007.

Human Genetics Commission Citizens Report, July 2008.

Biometrics: Enabling Guilty Men to Go Free? Further Adventures from the Law of Unintended Consequences - Jerry Fishenden blog post

Digital Decision Making: Back to the Future - chapters five and six
Ray Corrigan, Springer-Verlag

Study information and communications technologies with The Open University

At the end of November 2008, the world of which I am a part, became riveted by the events in Mumbai. A series of attacks occurred in South Mumbai – in the famous Chhatrapati Shivaji Rail Terminal, in two hotels – the Taj Mahal Palace and Tower, and the Oberoi Trident, in a Jewish centre – Nariman House, the Cama hospital and in the Leopold Café, among others. But it is the ongoing nature of the attack on the plush Taj Tower that captivated the media. The visual spectacle of the destruction of a Victorian building, where many foreign tourists lived and where many of the world’s famous designer outlets were located, evoked a world of past and present wealth, in threat, under attack.

The stories of Mumbai were widely covered by the world press. And there have been a range of commentators on various aspects of the coverage of the attacks, especially, the media focus on Taj, rather than the many other sites where ordinary people lost their lives. As Arundhati Roy remarked, the lives of some seemed to matter more than that of others.

However, what I want to remark on here is the way in which the pictures of 26/11 and the analysis then circulated through the media. One evening an Indian friend sent me a link to a set of television programmes on a Pakistani TV channel that claimed that 26/11 was indeed India’s 9/11.

The programmes said that just as the US had perpetrated the attacks on the World Trade Centre in order to justify attacking Iraq and Afghanistan, so too had India masterminded the attacks in Mumbai in order to kill the chief of the anti-terrorism squad, Hemant Karkare, who was due to pronounce that a Hindu-led political group was behind one of the bomb blasts earlier in India. However, the anchor and the guests on this channel claimed, the Indians were unable to conduct this home-made terrorism with the panache that the Americans had conducted 9/11.

I was not the only recipient of this link – it circulated widely on a range of email groups, was shown on Indian television and became a frequently discussed topic within the diasporic community. The large number of hits on its youtube page bear witness to its circulation.

It also provoked a range of responses from those who read it, particularly a degree of disbelief and anger at the stand taken in the programme. It led to familiar calls to stop the appeasement of Muslims in India, and of Pakistan more generally. A few people argued, as Roy has, that terrorism has its routes in past injustices, and economic deprivation, not (only?) religion or regional affiliation.

Yet, it also provoked in me questions of how to deal with this text that I was sent – do I delete the link, share it with our Pakistani friends, share it with our Indian friends, ignore it? The hour-long programme was clearly inflammatory, defamatory, but also thought-provoking about the possibilities of alliances, different interpretations, viewpoints. These questions of communication and of our responsibilities about what to say, when and to whom continue to haunt me as the airwaves abound with sympathy and solidarity with those who were killed in the attacks and more problematically with critique and counter-critique which masquerades as analysis of the attacks. These questions of mediation, of the multiple roles that the media play, what gets reported, how these reports then take on their own life, are re-reported, analysed and become the material for new rounds of angst is the stuff of our lives. This blog is another, and hopefully, a reflexive part of that stuff.

About the author

Parvati Raghuram is Lecturer in Geography at the Open University. Her research interests focus on the ways in which the mobility, of individuals, goods and of ideas is reshaping the world.

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