License plate reader searches should require a warrant

车牌识别系统的搜索应当需要搜查令

So while I work with police departments regularly, I think it is critically important that technology be used reasonably. While this may be off-putting to some of my clients, I worked with the Institute for Justice as an expert witness in their trial Schmidt v City of Norfolk. (Any opinions herein are my own and not those of IJ, to be clear.) The gist of that case was whether searches of historically cached ALPR data (automated-license-plate-reader) constituted an illegal search. The judge ruled against plaintiffs in that case.

尽管我经常与警察部门合作，但我认为合理使用技术至关重要。虽然这可能会让我的某些客户感到不快，但我曾作为专家证人参与了“施密特诉诺福克市案”（Schmidt v City of Norfolk），为司法研究所（Institute for Justice）提供支持。（需要明确的是，文中的任何观点仅代表我个人，不代表司法研究所。）该案的核心在于，对历史缓存的自动车牌识别（ALPR）数据进行搜索是否构成非法搜查。法官在该案中作出了不利于原告的裁决。

Here is a quote from the judgment: Consistent with Plaintiffs’ claims in this case and controlling precedent involving mass surveillance in public spaces, ALPR surveillance could become too intrusive and run afoul of [constitutional privacy standards] at some point. But when? While a definitive answer to that question is elusive, what is readily apparent to this Court is that, at least in Norfolk, Virginia, the answer is: not today. The important point to note about this quote is “not today”.

以下是判决书中的一段引文：“与本案原告的主张以及涉及公共场所大规模监控的既定先例一致，ALPR 监控在某些时候可能会变得过于侵入性，并触犯[宪法隐私标准]。但会是什么时候呢？虽然对该问题的明确答案难以捉摸，但本法院显而易见的是，至少在弗吉尼亚州诺福克市，答案是：不是今天。”这段引文中需要注意的关键点是“不是今天”。

This will be a long winded post, but to try to keep it simple: I think cameras will become ubiquitous in the foreseeable future. So the question is not if this data will require a warrant, it is when. It is going to happen eventually under current case law. I think cameras are good, and can be used to reduce crime in a cost effective manner. There is a difference between active flags (e.g. this car is stolen and it pings the PD when it drives past a camera) vs historical searches (e.g. look to see where license plate XYZ1000 was the last 30 days). Requiring a warrant for historical searches will not seriously impede police investigations.

这篇文章篇幅会很长，但简单来说：我认为在可预见的未来，摄像头将无处不在。因此，问题不在于这些数据是否需要搜查令，而在于何时需要。根据现行判例法，这终将发生。我认为摄像头是好东西，可以以经济高效的方式减少犯罪。我们需要区分“主动标记”（例如：某辆车被盗，当它经过摄像头时会向警局发出警报）与“历史搜索”（例如：查询车牌 XYZ1000 在过去 30 天内的行踪）。要求对历史搜索申请搜查令并不会严重阻碍警察的调查工作。

The current status quo of not retaining data is VERY BAD; it does not prevent illegal searches, and currently limits the utility of actually using that data for legitimate investigations. Current standards to prevent abuse of the searching ALPR data systems are laughable. Long story short in my opinion everyone would be better off if states just mandated warrant procedures through state statutes.

目前不保留数据的现状非常糟糕；它既不能防止非法搜查，也限制了将这些数据用于合法调查的效用。目前防止滥用 ALPR 数据搜索系统的标准简直可笑。简而言之，我认为如果各州能通过州法律强制执行搜查令程序，对所有人来说都会更好。

Current Legal Standards

现行法律标准

To try to not get too much into the weeds of what historically constitutes a search, I think the easiest place to start is via Carpenter vs US. So current US case law requires police departments to obtain a warrant to request cellular providers provide law enforcement with cell phone tower pings (cell-site location information, CSLI). This deviated from historical precedent in requiring a warrant mainly because it was private companies that had the information.

为了避免陷入关于“何为搜查”的历史细节泥潭，我认为最简单的切入点是“卡彭特诉美国案”（Carpenter vs US）。目前的美国判例法要求警察部门在请求移动运营商提供手机基站定位信息（CSLI）时必须获得搜查令。这偏离了历史先例，要求搜查令的主要原因是这些信息掌握在私营公司手中。

Before Carpenter, mostly it was argued you did not have a reasonable expectation of privacy if a private company could access the same data. The court in Carpenter basically made a determination that cell phone data was so comprehensive it justified a different standard – that you could track the whole of a person’s movements with the detailed CSLI data. And that this level of invasiveness violated a reasonable person’s expectation of privacy. Even if Google had all that info, you did not expect them to give it away.

在卡彭特案之前，人们普遍认为，如果私营公司可以访问相同的数据，那么你就没有合理的隐私预期。卡彭特案中的法院基本上认定，手机数据过于全面，因此需要不同的标准——即你可以通过详细的 CSLI 数据追踪一个人所有的行踪。这种程度的侵入性违反了一个理性人的隐私预期。即使谷歌拥有所有这些信息，你也不会期望他们将其泄露出去。

This opinion was reaffirmed with the recent Chatrie decision (for geofence warrants, e.g. give me a ping for all cell phones in area X and datetime-range Y). Another relevant decision to be aware of is also Beautiful Struggle v Baltimore, in which searching historical aerial imagery via drones also constituted a search. So this is why I am saying the question is when, not if, ALPR data will require a warrant. If a city happened to have a camera on literally every intersection (which I think will happen in the future), under current case law it would clearly be the same situation as you have for your cell phone data.

这一观点在最近的“查特里案”（Chatrie decision，涉及地理围栏搜查令，例如：提供 X 区域和 Y 时间段内所有手机的信号记录）中得到了重申。另一个值得注意的相关判决是“美丽斗争诉巴尔的摩案”（Beautiful Struggle v Baltimore），该案裁定通过无人机搜索历史航拍图像也构成搜查。这就是为什么我说 ALPR 数据需要搜查令是“何时”的问题，而不是“是否”的问题。如果一个城市恰好在每个路口都安装了摄像头（我认为未来会实现），根据现行判例法，这显然与你的手机数据面临的情况相同。

Cameras are Good

摄像头是好东西

To be brief, again I mostly work with police departments in my career and was a former crime analyst. I do think ALPR cameras are good investments, mainly because they are cheap enough to have a reasonable return on investment. (Note I do not think this about all police tech, I am particularly critical of the price tag for acoustic-gun-shot-detection.) So ALPRs are well under $3,000 per camera. The machine learning models, camera, and computation necessary to flag a plate when it passes can easily fit on current cell phones.

简而言之，我职业生涯中大部分时间都在与警察部门合作，并且曾是一名犯罪分析师。我确实认为 ALPR 摄像头是很好的投资，主要是因为它们足够便宜，能带来合理的投资回报。（注意，我并非对所有警用技术都持这种看法，我特别批评声学枪击检测系统的价格。）ALPR 摄像头的单价远低于 3,000 美元。识别车牌所需的机器学习模型、摄像头和计算能力，完全可以集成在当前的手机上。

The overall evidence that ALPRs reduce crime is pretty meh at the moment, but because they are so cheap they really only need to increase a few arrests per camera to likely have a positive return on investment. It is pretty hand-wavy, as we do not have estimates for the value of increased clearances I find persuasive. But I think saying “I would pay $500 to help solve one case” is on the low side if anything. So a single camera if it helps catch just a handful of crimes a year is likely in my opinion to be a positive ROI.

目前关于 ALPR 能减少犯罪的证据还比较平庸，但因为它们非常便宜，每个摄像头只要能多破获几起案件，就可能产生正向的投资回报。这虽然有些模糊，因为我们缺乏关于提高破案率价值的令人信服的估算。但我认为，说“我愿意支付 500 美元来协助破获一起案件”甚至还偏低了。因此，在我看来，如果一个摄像头每年能帮助抓获几起犯罪，它很可能就是一项正向的投资。

I think cameras in all public spaces are going to happen. Imagine Ring comes out with a nicer camera system for homeowners that has more comprehensive views around your house and is just as cheap. And we will ultimately be safer for it. So even for folks advocating that cities do not pay for Flock, this is coming anyway in the near future.

我认为在所有公共场所安装摄像头终将实现。想象一下，如果 Ring 为房主推出了一套更好的摄像头系统，能提供更全面的房屋周边视野，且价格同样便宜。最终，我们将因此变得更安全。所以，即使是那些主张城市不应购买 Flock（车牌识别服务商）服务的人，也无法阻挡这一趋势在不久的将来到来。