面对现实

面部识别技术

不平静的过去---和未来

作者：柯大為Dave Kopel
邁克爾 Mike Krause

当工人Rob Milliron2001年7月坐在坦帕城娱乐区吃他的午餐的时候，他没有想到的是想抓他的警察会来到他的车间，乘他吃饭不注意的时候把面部识别照相机（最热门的高科技监督安全技术）放在他身上。

被照相机扫描的Milliron脸出现在纽约时报及世界技术报告文章里。标题说："在坦帕，你可以隐藏那些说谎的眼睛"。后来，俄克拉马州的一个妇女看到照片，误以为Milliron是她受疏忽孩子指控的前夫就打电话给警察。说服警察相信他从未结过婚，也没有过小孩甚至没到过伯克拉马州后，他告诉彼得堡时报的记者说："他们让我感觉自己象个罪犯"Milliron如果知道这样一个事实也许会略感欣慰：由于警方工作普遍使用面部识别技术（FRT）,不只是他一人被错误地怀疑。FRT的支持者提供给美国人一个听起来不错的交易：为安全卖掉你的秘密。最令人安慰的是，9/11后，我们所有人都从机场安全看到穆罕默德Atta及其它人员的有条纹的照片。FRT支持者说，如果那些照相机被连在可能的犯罪数据上，攻击者就决不会带上飞机。

但是，现在被用于至少两个美国城市和整个英国的FRT是不可靠并无效的。最多，它给我们的街道带来了等同于运输部机场安全政策的高科技，但糟糕的是，如果FRT不断这样工作的话，真正的问题会出现。它会在未来产生一个无处不在的侦察照相机被警察用于远没有反恐怖分子重要的事务。

FRT通过把计算机数据和照片图象结合。照相机获取图象后，计算机程序计算你脸上80%的节点如眼距，鼻宽或眼窝深度及下颚线的长度。技术然后把这些节似的尺寸变成一个叫"脸孔"数字代码。据推测一个好的面部识别系统可以把站在照相机前的人配成包括数千万个"脸孔"的数据记录。支持者说，罪犯将没有地方躲藏。守法的公民也没有理由害怕。

但是很大程度上，FRT没有象预期的那样工作。坦帕的Milliron事件只是一连串的国家实施的面部扫描之一，9/11之前，面部扫描使用受到普遍的嘲笑或只有几个市政当局考虑，它们是坦帕，杰克逊维尔，佛罗里达和维吉尼亚。那时FRT是作为捉拿被通辑的罪犯，寻找逃跑者及失踪的人的工具投入市场的。但是引进到维吉尼亚的立法机关的措施是需要法官同意使用FRT证明才行。在坦帕，已经支持它的使用的国会会员们称他们被愚弄，并不了解他们所投票的东西。

随着恐怖者的袭击，一切似乎在改变。维吉尼亚立法机构取消了需要司法支持的议案。FRT公司的主管在国会前被证实并被智力及法律执行代理委托。Viisage技术总裁Tom Colatosti告诉记者："如果我们的技术被展开，恐怖分子被识别的可能性是很大的。"主要机场包括波士顿Logan,达拉斯国际贸易站和国际棕榈海滩已经安装了FRT检测版本。在9/11后的六个月时间股票市场下跌的时候，Visionics和Identix扫描公司看到了它们的股价分别上升了244%和197%（两个公司拿来合并，现在叫Identix.）

然而一个难以克服的事实仍然存在：FRT不起作用。三月，棕榈海滩国际机场在中央广场C安检点运行了视觉"Argus"检测面部识别系统（可以插入现存的闭路电视系统的版本）。十五个机场工作人员试图通过安全检查口.安全检查人员有250个脸孔数据，其中包括那15个测试者。四周期间，测试者试图958次通过安检口，面部识别系统455次阻止了他们。成功率仅占47%.最糟糕的是当普通旅客和其它机场工作人员通过扫描器时还出现1081次错误报警。经计算每小时有二到三次错误报警。

在实验中，那些触发错误报警的人们不必被拉到一边由警方审问。但想象一下如果他们真的这样做了会发生什么：在每个机场的中央广场，FRT对数以万计的人们使用被通辑的嫌疑者数据。每小时至少产生几十个错误。

如果你要是被拘留的一员会怎么样？警方把你带到审讯室后，你怎样证明自己所说的是真实的而不是一个使用假身份证的恐怖分子（或一个普通的逃亡者）。如果你是个机场警察，在知道大多数的嫌疑者事实上都是无辜的时，你怎样进行你的工作？

棕榈海滩检测不是笼罩在FRT上的唯一阴影。丹佛大学秘密基金的前总理理查德史密斯也做了"Facelt"视力检测，得到了同样令人不信服的结果。

史密斯发现灯光，眼镜及背景，照相机位置，面部位置和表情的变化都严重影响图象质量和系统功效。他断定机场要使用FRT需使用"灯光受到严格控制及旅客单行通过的特殊通道"旅客需被指导脱去帽子和向照相机方向直视。

这完全和那些卖FRT的支持者的声明及易受骗的媒体反复重申的事实不符。根据丹佛Post,"照片间你增了 200磅或显得单薄没关系，照相机会迅速识别你，当然除非你带上太阳镜或摆动你的头或是做鬼脸。"

一项国家标准技术学会的研究发现同一个人一年半后的照片错误率达43%，国防部投资的FRT商业可行测验结果是一样的。它发现系统三分之一以上的时间出错，制造大量的错误结论。你所听到的扫描公司极高的可靠率通常是基于最佳条件下的实验室检测。史密斯说"即使技术完美，它仍会让99%个恐怖分子通过 . . . 面部识别系统的最大问题是一个简单的事实：我们不知道谁是恐怖分子，法律执行也没有他们的照片。在机场定位恐怖分子只是这个技术的错误运用。"

即使我们知道谁是恐怖分子，我们必须让他们都坐下来和Annie Leibovitz开个FRT有用会议。根据棕榈海滩国际的测试者：输入的照片需要高质量以使照片匹配成功。同样被扫描的人需要站直，朝照相机直视及不戴帽子。因为棕榈海滩研究公认："测试者的头的运动会使系统能力产生很大影响，如果测试对象姿势偏离输入照相机焦点15到30度或带着眼镜，就会造成匹配的实质失败。"

集中脸部扫描在2001年1 月在坦帕的超级杯35决赛上，球迷的脸被秘密地用Viisage系统与已知的罪犯数据库对照而正式介绍给美国公众的。然后坦帕当局开始在Ybor城娱乐区使用扫描仪。他们以在街上徘徊或吃饭的人为目标，把他们的脸孔与罪犯及逃跑者数据对比。

在使用公开的记录请求下，美国民间自由协会（ACLU）发现系统在其首次公开宣传的数月就不行，没有正确和罪犯数据匹配，相反根据ACLU，系统把男女对象和年龄及体重有明显不同的对象匹配。

另一方面，FRT只能是个哑巴而不是检查员：即使他可以从女人中区分出男人，或从瘦高人中区分出矮胖人。坦帕警方否认他们已放弃FRT，说他们正在修补使之与更多的照相机工作。

在他们投这笔钱之前，他们应仔细看看FRT世界资本的经历。有25万人口的伦敦区的纽汉成为被支持者大肆吹捧为技术的证据。令人敬畏的制止犯罪能力。纽汉吹嘘近300个政府照相机被安置在战略位置并连接到视力Facelt系统。

提倡者吹嘘纽汉地方政府官员自1998年把犯罪率降到了40%.。这个结果如果是真的，显然不会长久。根据美国新闻国际报道，街头抢夺和汽车盗窃---两项据说是FRT最具威慑的----去年在纽汉又上升。

如Jeffrey Rosen去年十月在纽约时报杂志上所报告的，纽汉侦探系统在其三年运行期间，没有一次逮捕。运行系统的人甚至也不知道谁在数据里。它们的威慑力也许存在于粘贴于整个纽汉的通知，告诉罪犯照相机在监视，警方知道他们是谁，住在哪里以及他们所犯的罪行。当然，如纽汉监视长向Rosen承认的："这不是真的"。

纽汉只是英国二十世纪九十年代早期用于反恐怖分子轰炸伦敦金融区而发展的侦查照相机网络的一部分。英国现在已有一百五十万政府照相机投入使用。当照相机推出初期，政府在保守分子的控制下坚持："如果你没有什么要隐藏，那么你就没什么可害怕的。"现在在劳动党的控制下，政府正投资1.15亿美元购置更多的侦探照相机。

即使有了这些无处不在的照相机，英国的暴力及财产案件发生率仍在迅速上升。苏格兰中心一个为时三年的政府对犯罪学的研究最近断定没有迹象表明英国的侦探照相机的使用总体上降低了严重的犯罪率。另一个研究由关心安置罪犯国家协会对英国14个城市做调查，发现照相机对降低犯罪基本上没有什么作用。研究建议加强街道灯光会是一个更划算的犯罪预防措施。

这大多可说成是支持照相机：一些情况，他们被用于证明超速者及其它一些交通违规者还有乱丢垃圾者有罪。一件事是放弃你的秘密而捕捉爱尔兰共和国军队的恐怖分子。另一件是放弃秘密这样警察可以抓住乱丢垃圾的人。

当然仅因为FRT今天没有做好并不意味着它从不起作用。FRT公司正接收大量的社团福利。根据三月综合计算部（GAO）报告，截止到2001年六月，司法和国防部分别给了2100.3万美元，2400.7美元用于研究开发FRT。所有这些研究将可能最终会导致改良产品。

那么然后会怎么样呢？洛杉矶加州学院信息研究系的副教授Philip Agre反对道：随着FRT的改进，潜在的弊端会相应提高。"因为潜在信息和通信技术（数字照相机，图象数据，处理能力及数字通讯）会相当便宜（而更具功效）"他在他的网站上写道："有或没有那些面部被捕获的人们的同意，新的面部图象数据会不难被建立。"

一旦那些数据存在，他们的使用会随着典型的官僚政治团毫无疑问地扩展。看这个例子，2001年科罗拉多州法律允许发动机公司使用生物测量技术绘制申请者图？用于驾驶执照面容。据说这个意图是阻止同样一个人取得多个驾照。但是法律的语言更广泛，允许进入DMV数据"帮助联邦，国家或地方政府机构行使这样的官方功能机构"换句话说就是不管什么政府意图，伊利诺斯州和本维吉尼亚会把他们的司机执照局变成强制的脸孔集中点。

政府批评后，三月科罗拉多州立法机构优化了面部绘制方案宣布：在政府机构选择图象数据之前，它必须有"一个合理的怀疑即已构成犯罪或将构成犯罪及合理的怀疑要求的图象是这样一个罪行的作恶者或是这样一个罪行的受害者。"如科罗拉多州，政府可以建立指导方针在表面上限制政府使用你的脸孔。但是一旦你的脸孔在政府的数据里，联邦政府有权随意使用。根据联邦法令，每一个联邦机构都有每一个政府司机驾照记录。"包括任一个法院或执行其功能的法律行使机构"因为美国宪法的最高条款，国家政府不能限制使用联邦机构放置的国家收集的脸孔。

甚至在9/11之前，许多当地法律行使机构认为政治监督是他们官方功能之一。例如去年春天众所周知丹佛警察智能机构保存了政府抗议者文件数年，包括关于3000个个体及200个组织。这些警方监督的目标中有美国友情服务协会（一个教友派信徒团体），Amnesty国际组织及Copwatch(反对警察残暴团体).据推测，只是在秘密文件被科罗拉多民间自由协会关注后，这个监督项目才被拿掉（但并没有消除）

科罗拉多警察在进入脸孔数据前必须有"合理的质疑"听起来不错，但法律执行很容易这些限制周边的方法。丹佛警察指导方针一贯要求犯罪质疑，所以警察只简单地把他们想要监控团体列为极端分子。

的确，丹佛警察局政治监督项目的主要约束是人力。一时只有那么多警察可以侦察人们。但是有了FRT，政治监督会没有这个限制。考虑一个自动监测系统备有一个脸面扫描照相机，脸面识别软件及国家司机执照面孔数据。编辑一个参加抗议警方暴力集会，反抗药品法律或反对美国外交政策人员名单会是一个简单的事情。

必要的技术也不会被限制于使用在政治抗议上。2001七月，美国众议院保守派领袖Dick Armey(R-德克萨斯州)加入了ACLU警告说：联合使用脸孔识别软件 . . . .科罗拉多数据可以允许识别跟踪记录储存每一个公民的公开行动。听起来不自然？ 2001年9月20日是，Visionics的执行总裁Joseph Atick告诉机场安全委员会运输部：连在安全照相机上的Facelt可以通过网络连接到联邦监测中心并在数秒内向官员发出匹配报警。他又说，事实上，作为一个广大的数据网络，任何地方的任一个照相机都可以被连接到这个系统。

FRT的反对者不该指望太多的来自法院的帮助。标准法律教条支持在公众场合没有或无望有秘密。没有任何违反宪法的，如，警察坐在购物街的长椅上记录过往的行人。FRT提倡者争辩说，大块的监督只是象有10或100个警察在购物街。数量的差异不具重要意义。

然而即使我们知道电子政府眼睛与每个角落的警察完全相同，我们真的想要那个吗？Jeffrey Rosen在纽约时代杂志上关于英国侦察照相机做了这样一个结论：照相机的设计生产不是用来逮捕而是使人们感到他们随时都在被监视。"照相机后人们正上升的公开的非传统行为与恐怖主义无关."Rosen写道"也与反严重犯罪无关，照相机正以美国人想避免的方式，用于加强社会统一。"

有希望的一些理由，过去美国法院知道技术的变化会造成宪法的差异。在19世纪的宪法条款下，警察无需经许可就可以偷听。如果一个警察站在公众场所就可以听到屋子里的谈话，他就无需一个搜查证。那个条款在1800年代有意义;如果你的声音太大以至于人行道上的人都能听见，你对你所说的话没有秘密的法律期待。

但是1967年Katz事例美国最高法院考虑了没有侵入私人财产，使用类似扩音器或窃听装置收听交谈的警方提出的论点。正义的Hugo Black说，这种监督是允许的因为新的技术只是偷听的更新版本。但法院的大多数规定窃听装置和其它电子监督只有在警察得到了搜查证才允许。电子监督的插入，它的巨大的潜在弊端及对传统的秘密期待的侵害都能从过时的偷听中区分。

同样，普遍的脸孔扫描最终可以使政府有可能在大多数时间跟踪大部分市民的行动。它会通过几个数量命令增强政府的跟踪能力---就象人耳到类似于扩音器一样的巨增。

象第四次修正本身，Katz依靠主观的合理的判断。这样，没有保证Katz会反对无所不在的英国风格的脸孔扫描；Katz也无需禁止把关于每个人的行动信息放在永久的政府数据里。

最终，脸孔扫描的未来将取决于政治程序。美国大众及他们选举的官员会投票支持一直跟踪每个人几乎是不可能的。然而脸孔扫描在没有具体立法许可就被管理法令典型地介绍和扩大。

所以未来的美国极有可能从历史书中惊奇地了解为第一世纪的美国独立公民认为政府不会也不可以在公众场所监视他们的所有行为。

柯大為為研究主任，邁克爾為研究學會的高級會員。

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Face the Facts

Facial recognition technology's troubled past -- and troubling future.

By David Kopel and Michael Krause

When construction worker Rob Milliron sat down to eat his lunch in Tampa 's Ybor City entertainment district in July 2001, he didn't expect that it would result in a visit to his workplace by police officers looking to arrest him. His innocent dining inadvertently placed him in a showcase for one of the hottest trends in high-tech surveillance security: facial recognition cameras.

Milliron's face, scanned by the cameras, ended up in a U.S. News & World Report article about the technology. The accompanying headline read: "You can't hide those lying eyes in Tampa." Then a woman in Oklahoma saw the picture, misidentified Milliron as her ex-husband, who was wanted on child neglect charges, and called the police. After convincing police he had never been married, had kids, or even been to Oklahoma, he told the St. Petersburg Times, "They made me feel like a criminal."

Milliron perhaps can take some comfort from the fact that, as the use of facial recognition technology (FRT) for police work spreads, he won't be alone in being falsely suspected. FRT advocates offer Americans a sweet-sounding deal: sell your privacy for security. That's an especially comforting pitch in the wake of 9/11. We've all seen the grainy photos of Mohammed Atta and crew waltzing through airport security. If only those cameras had been linked to the proper criminal databases, say FRT proponents, the attackers never would have made it onto the planes.

But FRT, currently used in at least two U.S. cities and widespread throughout Great Britain , is notoriously unreliable and ineffective. At its best, it brings to our streets the high-tech equivalent of the Department of Transportation's airport security policy: humiliate and search everyone ineffectively.

That's bad enough, but the real problems will occur if FRT ever does start working as promised. It threatens to create a creepy future of ubiquitous spy cameras that will be used by police for purposes far less noble than thwarting terrorists.

FRT works by combining photographic images with computer databases. After an image is captured by a camera, a computer program measures some of the 80 or so nodal points on your face, such as the distance between your eyes, the width of your nose, the depth of your eye sockets, and the length of your jaw line. The technology then turns the nodal measurements into a numerical code called a "faceprint." A properly working face recognition system supposedly can match a person standing in front of a camera with a record from a database including tens of millions of faceprints. Criminals, say proponents, would have nowhere to hide. And law-abiding citizens would have no reason to fear.

Yet for the most part, FRT hasn't worked as intended. The Milliron incident in Tampa was just one of a string of national flops for face scanners, which prior to 9/11 were widely derided even as they were being implemented or considered by several municipalities, including Tampa; Jacksonville, Florida; and Virginia Beach, Virginia. At the time, FRT was being marketed as a tool to catch wanted felons and find runaways and missing persons. Nonetheless, a measure was introduced in the Virginia legislature requiring a judge's approval to use FRT, and in Tampa city council members who had approved its use claimed they had been fooled and didn't know what they had voted for.

Then the terrorists attacked, and everything seemed to change. The Virginia legislature dropped the bill requiring judicial approval. Executives at FRT firms testified before Congress and were called on by intelligence and law enforcement agencies. Tom Colatosti, CEO of Viisage Technology, told reporters, "If our technology had been deployed, the likelihood is [the terrorists] would have been recognized." Major airports, including Boston 's Logan, Dallas-Fort Worth International, and Palm Beach International, have installed test versions of FRT. While the stock market was slumping, scanning companies Visionics and Identix saw their share prices shoot up 244 percent and 197 percent, respectively, in the six months following 9/11. (The two companies have since merged and are now known as Identix.)

Yet one stubborn fact remains: FRT doesn't work. In March, Palm Beach International Airport ran a test of Visionics' "Argus" facial recognition system (a version that can be plugged into existing closed circuit TV systems) at its Concourse C security checkpoint. Fifteen airport employees tried to get through the security checkpoint. The security checkers had a database of 250 faceprints, including those of the 15 testers. Over a four-week period, the testers made 958 attempts to pass through the checkpoint; the face recognition system stopped them 455 times, for a success rate of only 47 percent. On top of that, there were 1,081 false alarms triggered by ordinary passengers and other airport employees passing through the scanners. That worked out to two or three false alarms per hour.

In the experiment, the people who triggered false positives didn't have to be pulled aside and interrogated by the police. But imagine what would happen if they did; imagine FRT on every concourse of the airport, using a database of "wanted" suspects numbering in the hundreds of thousands. That would make for at least dozens of false positives every hour.

What happens if you're one of the folks detained? After the police have marched you into the interrogation room, how do you prove that you're really who your identification says you are, and not a terrorist (or an ordinary fugitive) using false ID? If you're one of the airport cops, how do you go about your job knowing that the overwhelming majority of the suspects are in fact innocent?

The Palm Beach test isn't the only one that casts a shadow on FRT. Richard Smith, former head of the Privacy Foundation at Denver University and now a privacy and Internet security consultant in Brookline, Massachusetts, conducted his own test of the Visionics'"FaceIt" system. He got similarly unimpressive results.

Smith found that changes in lighting, eyeglasses, background objects, camera position, and facial position and expression all seriously affected image quality and system efficacy. He concluded that airport use of FRT would require "special walkways where lighting is tightly controlled and passengers pass single file." Passengers would have to be "instructed to remove hats and glasses and look straight ahead at a head-height camera."

None of this fits with the exaggerated claims in favor of FRT made by those selling it and repeated as fact by gullible media outlets. According to the Denver Post, "It doesn't matter if you gain 200 pounds or go bald between photographs. Short of plastic surgery the camera will recognize you." Unless, of course, you put on sunglasses, or cock your head, or make a funny face.

Or get older. A study by the National Institute of Standards and Technology found a 43 percent failure rate for pictures of the same person taken one and a half years apart. Similarly, the Defense Department funded a test of commercially available FRT. It found that the systems failed one-third of the time and produced a large number of false positives. The impressive reliability rates you hear from the face scanning companies are usually based on tests in laboratories under optimal conditions.

Yet "even if the technology worked perfectly," Smith observes, "it would still allow 99 percent of the terrorists through....The biggest problem with face recognition systems is the simple fact that we don't know who the terrorists are and law enforcement doesn't have their pictures. Spotting terrorists at airports is simply the wrong use of this technology."

Even if we did know who the terrorists were, we'd have to sit them all down for a session with Annie Leibovitz for FRT to be useful. According to the testers at Palm Beach International, "Input photographs needed to be of good quality to make successful matches." Similarly, people being scanned need to stand still, look straight at the camera, and not wear glasses. As the Palm Beach study acknowledged: "Motion of test subject head has a significant effect on system ability. There was substantial loss in matching if test subject had a pose 15 to 30 degrees off of input camera focal point and eyeglasses were problematic."

Mass face scanning was formally introduced to the American public in January 2001 at Super Bowl XXXV in Tampa, when football fans had their faces surreptitiously checked with a Viisage system and compared to a database of known criminals. The Tampa authorities then began to use scanning in the Ybor City entertainment district. They targeted people strolling down the street or eating lunch, comparing their faceprints to a database of criminals and runaways.

Using open record requests, the American Civil Liberties Union (ACLU) discovered that the system was essentially abandoned within months of its highly publicized rollout. No correct matches had been made to the criminal database. Instead, according to the ACLU, the system matched "male and female subjects and subjects with significant differences in age and weight."

Put another way, FRT can be dumber than Inspector Clouseau: Even he could distinguish a man from a woman, or a short fat man from a tall thin man. The Tampa police, for their part, deny they have abandoned FRT, saying they are revamping it to work with more cameras.

Before they spend the money, they should take a closer look at the experience in the world capital of FRT. The London borough of Newham, with a population of about 250,000, is widely touted by advocates as proof of the technology's awesome crime-fighting ability. Newham boasts approximately 300 government cameras located in strategic places and linked to Visionics' FaceIt system.

Newham's FRT is credited by advocates and local government officials with cutting crime by nearly 40 percent since 1998. That effect, if real, was apparently not long-lasting. According to a United Press International report, street robberies and car theft -- two crimes for which FRT is supposed to be an especially powerful deterrent -- were on the rise again in Newham last year.

And as Jeffrey Rosen reported in The New York Times Magazine last October, the Newham spy system has not resulted in a single arrest during its three years of operation. Nor do the people who run the system even know who is in the database. The deterrent effect, to the extent there may be one, appears to lie with the signs posted throughout Newham telling criminals that cameras are watching and that the police know who they are, where they live, and what crimes they have committed. Of course, "it's not true," as the Newham monitoring chief admitted to Rosen.

Newham is simply a part of Great Britain's growing spy camera network, which arose as a response to terrorist bombings in London's financial district in the early 1990s. Britain now has some 1.5 million government cameras in place. As the cameras were first being set up, the government, then under the control of the Tories, insisted that "if you have nothing to hide, you have nothing to fear." Now under control of the Labour Party, the government is spending $115 million for still more spy cameras.

Despite ubiquitous cameras, however, violent and property crime in England is soaring. A three-year government study by the Scottish Center for Criminology recently concluded there is no evidence to suggest that Britain's spy cameras have reduced serious crime overall. Another study, this one by the National Association for the Care and Resettlement of Offenders, looked at 14 British cities and found that the cameras had little effect in reducing crime. The study suggested that improving street lighting would be a more cost-effective crime prevention method.

This much can be said in favor of the cameras: In some cases, they have been used to convict speeders, other traffic law offenders, and litterbugs. Yet it's one thing to give up your privacy to catch Irish Republican Army terrorists. It's another thing to surrender privacy so the police can catch people who litter.

Of course, just because FRT doesn't work very well today doesn't mean it will never work. FRT companies are receiving massive amounts of corporate welfare. According to a March General Accounting Office (GAO) report, as of June 2001 the Departments of Justice and Defense had given about $21.3 million and $24.7 million, respectively, to the research and development of FRT. All this research will probably result in much-improved products eventually.

What then? Philip Agre, an associate professor in the Information Studies Department of the University of California at Los Angeles, argues that as FRT gets better the potential for abuse will rise commensurately. "As the underlying information and communications technologies (digital cameras, image databases, processing power and data communications) become radically cheaper (and more powerful)," he writes on his Web site, "new facial image databases will not be hard to construct, with or without the consent of the people whose faces are captured."

Once those databases exist, their uses will doubtless expand, consistent with typical bureaucratic mission creep. Look, for example, at the 2001 Colorado law allowing the Division of Motor Vehicles (DMV) to use biometric technology to map applicants' faces for driver's licenses. The stated intent was to stop the same person from obtaining multiple licenses. But the law's language was much broader, allowing access to the DMV database to "aid a federal, state or local government agency in carrying out such agency's official function" -- in other words, for any government purpose whatsoever. Illinois and West Virginia also have turned their driver's license bureaus into mandatory faceprint collection points.

In March, after national criticism, the Colorado legislature refined the face mapping scheme, declaring that before a government agency can tap into the image database, it must have "a reasonable suspicion that a crime has been committed or will be committed and a reasonable suspicion that the image requested is either the perpetrator of such a crime or the victim of such a crime." Like Colorado , states can establish guidelines that ostensibly limit government use of your faceprint. But once your faceprint is in a state database, the federal government has legal authority to use it for any purpose at all. By federal statute, every state driver's license record is available to every federal agency, "including any court or law enforcement agency, in carrying out its functions." Because of the Supremacy Clause of the U.S. Constitution, a state government cannot limit the uses to which federal agencies put these state-gathered faceprints.

Even before 9/11, many local law enforcement agencies considered political surveillance to be one of their official functions. For example, last spring it came to light that the Denver Police Intelligence Unit has for years kept surveillance files on government protesters, including about 3,000 individuals and 200 organizations. Among those targeted for police spying were the American Friends Service Committee (a Quaker group), Amnesty International, and Copwatch (a group that protests police brutality). The surveillance program was supposedly scaled back (though not eliminated), but only after secret documents were brought to public attention by the Colorado Civil Liberties Union.

Telling Colorado cops that they must have "reasonable suspicion" before accessing the faceprint database sounds good, but law enforcement will easily find ways around such restrictions. The Denver police surveillance guidelines have always required criminal suspicion, so the police simply listed as extremists the groups they wanted to spy on.

Indeed, the main constraint on the Denver Police Department's political spying program was manpower. There are only so many people a police unit can spy on at once. But with FRT, political surveillance may one day escape such limits. Consider a mobile monitoring unit equipped with a face scanning camera, face recognition software, and the state's driver's license faceprint database. It would be a simple matter to compile a list of everyone who attends a rally to protest police brutality, to denounce drug laws, or to oppose U.S. foreign policy.

Nor will the technology necessarily be confined to use at political protests. In July 2001, the conservative U.S. House Majority Leader Dick Armey (R-Texas) joined with the ACLU to warn: "Used in conjunction with facial recognition software...the Colorado database could allow the public movements of every citizen in the state to be identified, tracked, recorded and stored."

Sound far-fetched? On September 20, 2001, Joseph Atick, CEO of Visionics, told a Department of Transportation airport security committee that FaceIt, in conjunction with security cameras, could be linked via the Internet to a federal monitoring station and alert officials to a match within seconds. He added that virtually any camera, anywhere, could be linked to the system, as could a "wide network of databases."

Opponents of FRT should not count on much help from the courts. Standard legal doctrine holds that there is little or no expectation of privacy in public. There is nothing unconstitutional, for example, about a police officers sitting on a bench at a shopping mall and making notes about the people who pass by. FRT advocates can argue that massive surveillance is simply like having 10 -- or 100 -- police officers in the mall, and that the quantitative difference is of no constitutional significance.

Yet even if we acknowledge that electronic government eyes are no different than a cop on every corner, do we really want that? One of the conclusions of Jeffrey Rosen's New York Times Magazine piece on spy cameras in Great Britain was that the cameras are designed not to produce arrests but to make people feel they are being watched all the time. "The people behind [the cameras] are zooming in on unconventional behavior in public that has nothing to do with terrorism," Rosen wrote. "And rather than thwarting serious crime, the cameras are being used to enforce social conformity in ways that Americans may prefer to avoid."

There is some reason for hope, however. In the past, U.S. courts have acknowledged that technological change can make a constitutional difference. Under 19th-century constitutional doctrine, there was no need for the police to get a warrant before eavesdropping. If a policeman stood on public property and could hear a conversation going on inside a house, he did not need a search warrant. That doctrine made sense in the 1800s; if you talk so loudly that people on the sidewalk can hear you, you don't have a legitimate expectation of privacy for your words.

But in the 1967 case Katz v. United States, the Supreme Court considered the issue raised by police officers who, without trespassing on private property, used parabolic microphones or wiretaps to listen in on conversations. Justice Hugo Black said this kind of surveillance was permissible because the new technology was simply an updated version of eavesdropping. The majority of the Court, however, ruled that wiretaps and other electronic surveillance should be permitted only if the police obtained a search warrant. The intrusiveness of electronic surveillance, its great potential for abuse, and its infringement on traditional expectations of privacy all distinguished it from old-fashioned eavesdropping.

Similarly, widespread face scanning could eventually make it possible for the government to track the movement of most citizens most of the time. It would expand the government's tracking capability by several orders of magnitude -- as great an increase as the one from human ears to parabolic microphones.

Like the Fourth Amendment itself, Katz relies on a subjective judgment of reasonableness. Thus, there is no guarantee that Katz would stand as a barrier to omnipresent British-style face scanning; nor would Katz necessarily forbid placing information about every person's movements in a permanent government database.

Ultimately, the future of face scanning will depend on the political process. There is almost no chance that the American public or their elected officials would vote in favor of tracking everyone all the time. Yet face scanning is typically introduced and then expanded by administrative fiat, without specific legislative permission.

So there is a strong possibility that future Americans will be surprised to learn from history books that in the first centuries of American independence citizens took for granted that the government did not and could not monitor all of their movements and activities in public places.

David Kopel is research director and Michael Krause is a senior fellow at the Independence Institute.