快猫短视频

EVERY DAY, every minute, video cameras scan the crowds in a busy shopping
centre. But this is no ordinary public surveillance system. The faces of all
those passers-by are being converted into digital code and processed by
computer. Continuously, instantaneously, the facial code of each stranger is
compared with that of several dozen local criminals. If there is a match, an
alarm sounds in a control room, a human operator double-checks the computer鈥檚
assessment and alerts the police. Someone they want to keep tabs on, or someone
they want to arrest, is in town鈥�

This is not a scene from some Orwellian future. The system has been running
for a year on the streets of Newham in East London鈥攖he first trial of its
kind in the world. And the potential this kind of system doesn鈥檛 stop there.
Last month, several large stores in Regent Street, London, began using a system
that includes a database of convicted shoplifters who operate in the area. When
a store detective catches someone they think has been stealing and takes them to
the manager鈥檚 office, a camera mounted on the wall captures their face, which is
automatically checked against the database. You would also expect this
technology to be leapt on by state security services, such as those unseen
watchers who scan airport crowds for terrorists and drug smugglers. And sure
enough, a face-recognition system devised by Neurodynamics, a company based in
Cambridge, England, is being tested in secret at a British airport.

Facial recognition technology creates new opportunities for companies and
government agencies that want to keep tabs on people. But it is an infant
technology which some fear may be trying to run before it can walk. Is it
reliable enough to be used in such a sensitive field as public safety? And have
our rights to privacy been adequately debated?

We are our faces. To our fellow human beings, if not to ourselves, they are
the key identifiers. Our brains have exquisite machinery for processing and
storing a particular arrangement of eyes, nose and mouth and for picking it out
from other very similar arrangements. This ability is now being passed on to
computers.

True, facial recognition systems have worked for years under ideal conditions
in labs. But they are now moving out. Recent increases in processing power and
improved algorithms can give even fairly ordinary PCs the ability to capture
faces in the hustle and bustle of the real world. They can spot people who are
on the move and are not facing square on to the camera, and they can compensate
for changing light levels. Visionics of New Jersey, the company behind the
trials in Newham and Regent Street, claims that its technology is not even
fooled by hats, spectacles, beards and moustaches (see 鈥淚 see you鈥�).

We know who you are

Surveillance is not the only way this technology can be used. In fact much of
the impetus behind it comes from a different branch of the security
industry鈥攐ne which wants ways to make sure we are who we say we are.
鈥淏iometric鈥� features such as faces, fingerprints, irises, hand geometry and DNA
are powerful identifiers, and facial recognition offers important advantages
over its rivals. It is remote, quick and convenient鈥攖he machine equivalent
of a cool glance from a stranger. Many people don鈥檛 like having to touch things
that thousands of others have fingered and they are certainly not keen on
parting with bodily fluids.

So, when employees in Texas withdraw their pay cheques at hole-in-the-wall
cash machines, a camera and computer make sure that their faces and PIN codes
match. On the Mexican border, people can 鈥渇ast track鈥� their way into the US
after submitting their faces to automated scans. And in Georgia, digital images
of applicants for a driving licence are checked against the facial codes of the
millions of other licence-holders. (The system has already detected the same
face on more than a dozen different licences.) But what is so special, and
slightly sinister about facial recognition technology is that people need never
know that their identity is being checked, which is where many surveillance
projects begin.

The project in Newham is slightly different in that the local council and
London鈥檚 Metropolitan Police want criminals to know they鈥檙e being watched. The
system works by picking out as many faces as possible from passing crowds,
demonstrating that it has 鈥渁cquired鈥� a face by placing a red ring around it on a
monitor in Newham鈥檚 closed circuit television control room. If the software
finds a good match between that face and one in its database of mug shots, the
ring turns green and an alarm sounds.

On another screen, a close-up of the face on the street flashes up alongside
that of the criminal. Then human judgment comes into play. Only if Newham鈥檚
civilian operator in the control room considers that the two faces are identical
does she or he phone the local police station. For the police, the system is a
potentially useful tool for gathering intelligence about local villains as much
as a way to locate wanted criminals.

Before the Visionics system, called FaceIt, went live last October, Newham
carried out tests to see if it could detect staff members whose images had been
placed on the database. They paraded before the cameras wearing hats, glasses
and other disguises, but the software still recognised them. Since the system
went live, however, it has succeeded in identifying only two criminals on its
database walking the streets of Newham. In both instances, the police decided
not to make an arrest.

There are two possible explanations for this low detection rate. The first is
that villains were so alarmed when they heard about this new crime-fighting
technology that they decided to stay away and have done so ever since. The
second is that criminals are still coming into the area but the system isn鈥檛
spotting them. Bob Lack, Newham鈥檚 head of security, is hedging his bets on which
explanation is correct. He is delighted that crime in the target area has fallen
and believes it could be acting as a deterrent. But he also accepts that the
software still needs improving. Criminals do, it seems, have a good chance of
going undetected, although not surprisingly Lack and the Metropolitan Police are
reluctant to discuss this.

FaceIt was initially attached to only six of the 154 video cameras scanning
Newham鈥檚 streets, and it does not acquire every face 鈥渟een鈥� by those six. So
what was originally intended as a six-month trial has been extended, apparently
indefinitely. The aim is to have it linked to more cameras and adapted for
鈥渕ulti-heading鈥濃�� acquiring three faces at a time from the passing crowds.
Newham is seeking Home Office funding for this expansion; in the meantime, the
system remains operational.

Lack is keen to stress the multitude of measures designed to prevent the
system being abused. The control room is closely guarded and the digitised faces
of men and women in the streets are discarded as soon as the system finds no
match. Furthermore, the control room operators see only the faces of criminals
on the database: they do not see their names or records. That information stays
with the police, who will not say who is on the database or even how many
offenders are included.

Nothing to fear?

An internal police committee chooses the list of names, which probably
embraces paedophiles and drug dealers as well as violent robbers and burglars.
David Holdstock, a spokesman for the Metropolitan Police, says people convicted
of trivial offences, or who were not regarded as active criminals, would never
go on the database. 鈥淚t鈥檚 pretty focused and pretty targeted,鈥� he said. 鈥淚f
you鈥檙e innocent you have nothing to fear.鈥�

Others are not convinced by this reassurance. When the project began, the
Metropolitan Police reckoned that the system made accurate matches in 80 per
cent of cases, says Liz Parratt of Liberty, Britain鈥檚 council for civil
liberties. 鈥淚 see that as a 20 per cent failure rate,鈥� she says. 鈥淭hat鈥檚 an
unacceptable level of error.鈥� How many innocent people must have their collar
felt for every criminal caught?

There鈥檚 also the more general issue of whether we are watched enough already.
Britain has become the surveillance capital of Europe, with cameras in virtually
every city and large town, and many smaller ones. 鈥淓veryone wants to see crime
fall,鈥� says Parratt, 鈥淏ut I鈥檓 not sure I want to live in a society in which when
I walk down the road my face is compared with a couple of hundred local
肠谤颈尘颈苍补濒蝉.鈥�

Robin Wales, the elected leader of Newham Council, sees things the other way
round. 鈥淭here is a civil liberties issue at stake here,鈥� he says. 鈥淚t鈥檚 the
right of our citizens to live in Newham without fear of crime.鈥� He claims
widespread local support for its decision to introduce the technology.

Britain鈥檚 Data Protection Registrar, whose task is to protect the interest of
individuals against data collectors, has scrutinised Newham鈥檚 system and is
satisfied with the safeguards. But what happens next might be a problem. If the
trial is eventually pronounced a success in reducing crime then it may well be
extended to other public surveillance systems, first in Britain and then
elsewhere. And if these systems share a large, common database then criminals on
it would, in effect, be 鈥渆lectronically tagged鈥�. The police would know whenever
they showed their faces in any place covered by cameras.

Clearly this could be a powerful deterrent to crime, but it would take us a
big step nearer to a world in which Big Brother really is continuously watching
everyone. 鈥淲e would have serious concerns about such a general system,鈥� says
Jonathan Bamford at the Office of the Data Protection Registrar. 鈥淲e think it
would be inappropriate.鈥� After all, the decision to sentence offenders to be
electronically tagged, which gives the authorities a constant check on their
location, is made by the court, not the police.

So the spread of this technology raises an old but important question: who
guards the guardians? The actions of police, other state authorities and private
companies in compiling and maintaining face databases needs to be kept under
scrutiny. How serious a crime do you have to commit before your face goes on a
system? How long do you have to stay clear of crime before your face is removed?
Do you have the right to know that you are on a database? In Newham, there has
been no debate about these issues.

These questions are not just of interest to the criminally-inclined. A small
but fast growing number of PCs are sold with an integral video camera facing the
operator. One potential use for this is to check a person鈥檚 identity when they
log on to a network or try to buy something over the Internet. Chris Solomon,
who works on facial recognition at the University of Kent in Canterbury,
believes this kind of security system will be commonplace within a few
years.

Visionics鈥� rival Miros, a company based in Wellesley, Massachusetts, is
already marketing software that gives access to secure Web servers only to those
who have registered their faces. Solomon sees great advantages and a host of
applications in the technology. 鈥淏ut there are concerns,鈥� he says. 鈥淟ike so many
things in life, it鈥檚 a stick with two ends.鈥�

BOTH in grey matter and in silico, facial recognition is a two-stage process.
First you need to detect that a face is in the visual field. Then you need to
lock onto it and rapidly compare it with a database of thousands of faces in
memory. This process needs to allow for the fact that faces differ from moment
to moment and year to year. The most obvious source of variation is the angle
from which it is seen, but there are others, from changing light levels and skin
tones to expressions and facial hair.

Our brains overcome these confusions, allowing us to recognise a face with
astonishing rapidity, along with a host of accompanying
information鈥攆avours owed or owing, character assessment and (if we鈥檙e
lucky) a name. Algorithms capable of mimicking this astonishing ability, at
least in part, improved through the 1990s. Increases in computing power and the
reduction in cost of computers and video technology is starting to make facial
recognition affordable.

Several different approaches to automatic face recognition have emerged. One
builds up a person鈥檚 face by overlaying many different facial types, known as
eigenfaces. A computer varies the brightness of every eigenface in turn until it
finds a combination that resembles the face. The set of numbers representing the
brightnesses of the eigenfaces can then be compared with other sets stored in memory
(Sleuth City, 快猫短视频 supplement, 4 October 1997, p1).

The Visionics system, deployed in Newham, works by dividing up the image of a
face into between 12 and 40 elements, such as the outer corners of the eyes, tip
of the nose and ends of the eyebrows. It then measures the distances between
these elements, and gauges the angles between lines that are drawn between them.
These numbers become the digital identity of a face. The software can compensate
for head movements and changes in expression because it 鈥渒nows鈥� that the
elements can move slightly relative to one another.

The system focuses on a triangle between the base of the nose and the outer
edges of the eyebrows so, say the company, moustaches and beards do not confuse
it. Nor, it claims, do spectacles鈥攗nless heavy shades or glare occludes
the eyes. Faces can be turned up to 15 degrees away from the camera without any
loss of recognition performance. Once that angle is exceeded, its ability to
identify starts to deteriorate.

Of course, before the work of recognising can begin, the system has to find a
face within the video camera鈥檚 field of view. It does this with another set of
pattern-matching algorithms which detect 鈥渉ead-shaped鈥� objects in the field of
view. Then, once a face has been detected, it is 鈥渘ormalised鈥� to compensate for
variations in lighting condition, size (or distance from the camera) and skin
colour. This is rather like taking a photograph of a crowd, enlarging each face
in it to fill the same size of frame and adjusting the contrast and the average
shade of each to standard values.

What can you do to fool a face recognition system? Sporting a bag over your
head might arouse suspicion. Wearing heavy shades and a daft expression would
almost certainly throw the software off the scent, but you鈥檇 just have to hope
that you didn鈥檛 bump into someone you knew.