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License Plate Scanners: When Should Public Information Be Private?

By Mark Wilson, Esq. | Last updated on

The Los Angeles Police Department has about 242 cameras mounted on police cars throughout its fleet. That's not unusual, but the cameras are always on and always scanning license plates as they drive by. The cameras are connected to optical character recognition (OCR) software that reads and stores the license plate numbers -- every license plate that it sees, whether or not the plate is expired or the car's registrant is suspected of a crime.

A little creepy? The ACLU of Southern California thought so too, so it filed a records request to see a week's worth of license plate data from those cameras. The LAPD opposed it on the ground that it could reveal patrol patterns, which could impact current investigations; a superior court judge agreed with the LAPD.

The question remains whether collecting such information could be a search because the information -- license plate numbers -- is "in public" already.

Public v. Private

Asking what is public and what is private in an era where technology allows robots to track one's movements with pinpoint precision every minute of every day seems to be asking the wrong question. It requires going back to first principles, as Chief Justice Roberts did in Riley v. California.

When we use the language of the Fourth Amendment, what is it that we're protecting? Is it literally only "persons, houses, papers, and effects"? Probably not: Those are only examples of "things we'd rather the rest of the world didn't know about." That category is much broader than "public" and "private"; those words describe, generally, where things happen. What we're really concerned about is the nexus between the character of the things we're doing, regardless of where they're occurring, and the way those things are being tracked.

Even things occurring in public can be private in character, like a whisper between two people in the middle of a town square. If police have set up a listening post in the middle of the square that can capture every sound, including a whisper, then suddenly there are no more public-private moments. Likewise, parking one's car on a public road is something concededly happening in public, but automatically recording the location of a person's license plate wherever he or she is on the road, and then forming a map of where that person has been, exceeds the reasonableness of "the way those things are being tracked."

The Nexus Between Location and Method

This is probably why the LAPD's scheme seems viscerally creepy. Within seconds, a camera records a license plate number and the location of that license plate. It sends that information to headquarters, where a computer can use that information to create a map of everywhere that car has been. It can correlate those locations with locations of other known people, creating a database of private information by putting together "public" information.

Police do this all the time, but manually, with the limited capacity of their human brains. When a computer does it, it happens in seconds or minutes with perfect accuracy. The Fourth Amendment expects humans to make mistakes. Computers don't make mistakes, they don't take breaks, they don't need lunch, they don't go on vacation, they don't fall asleep. They're always watching, always listening, always correlating, building those networks of your intimate associations, crafting an accurate hypothesis of your private life based on information hidden in plain sight.

Does that sound "reasonable"?

What do you think about the public/private divide? Does "public" information have any protection? Join the discussion on Facebook at FindLaw for Legal Professionals.

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