How Automatic License Plate Recognition (ALPR) technology works

An officer from the Long Beach Police Department shows how automatic license plate recognition technology works. He demos a system installed in a patrol car equipped with four cameras. "Each camera is recording at all times, so no matter what mode you're in, it'll be recording off all four of the cameras… it shows you a picture the car, it shows you a picture of the plate that it caught and then what it does is it takes that image and using optical character recognition it will compare it to a database. In our case we are running multiple databases -- we have 'wanted felony vehicles,' 'be on the lookout,' '24 hour hotsheet,' 'wanted by detectives,' 'LA County warrants,' and our 'gang unit.' In addition to this we have 'stolen vehicles,' which are available to everybody in the state. Currently in our database we have 24,000,000 plus reads."

They also have a "parking scofflaw" database. "If a car has five or more outstanding parking tickets, state law allows us to tow it. And that turns into a revenue generator for the city… we have generated in excess of $3 million dollars."

The cheerful music licensed to accompany this promotional video is there to assure you that this technology is being used for public safety. (Via Doobybrain)


  1. This thing is primarily going to be used as a Revenue Generator and not for Public Safety no matter what they say if they can use it to maximize their profits they will.

    1. Ya but it’s revenue from assholes that are parked illegally no? Fine by me, especially consider the massive debt of most cities.

      And I must say I benefited from these things. A month ago my car was towed and moved by the gas company (PGW, bunch of bastards) and placed a mile away, I called them up seeing as it was a work site…they denied they moved my car! I figured it was stolen, called up the cops and a police officer showed up and found my car in the database within minutes. Not too shabby. As long as they’re used legally, these things just do what cops normally do…but faster.

      1.  Here in LA the parking rules range from silly to super ridiculous and the signs are often purposely confusing or misleading. I’d say that (at least in my neighborhood) 90% of the people getting ticketed are not being assholes in any way, shape or form.

    2.  Seriously, revenue generation is all cops do now. The guy even seems proud of that fact.  Maybe they wouldn’t need to generate so many millions if they weren’t having to pay out millions every year for settlements for wrongful arrests and beating the living shit out of people.


  2. Before this a cop basically called in a licence plate and someone looked it up manually on these databases.  The only real difference I see, from a civil liberties perspective (if there is one) is that the decision to run plates is no longer based on the race of the driver, unless they somehow have “racial recognition” software running as well.

    1. Truthy, apart from the fact that Officer John Henry, the hard-working racist cop, would need to scan several thousand plates an hour to compete with the automated system. 

      However, the civil-liberties concern here isn’t so much about protecting an individual from a bad cop.  The concern is that in a “Free Country”,  we were once allowed to go about our daily lives without the government compiling extensive records of our movements and whereabouts.

    2.  Well I think the concern is that the technology can be used to look at the comings and goings of those NOT suspected of a crime.  So the there are two big questions.  How EXACTLY are names put on the list, could “wanted by detectives” mean “what is my wife up to?” Also, does the system save info about the locations of cars that AREN’T listed?

  3. Facial Recognition Coming Soon!  Ask your ALPR Dealer!

    (also, I wonder if the Business Analyst that wrote up the spec originally titled the software LARPER…  now /that/ would’ve been a dandy.)

  4. The snark is easy, but the idea that a cop should be able to automaticaly ID a stolen car makes sense to me.

    The privacy and civil liberties issues are not ones of technology but ones of policy. The solution to a crippled and unaccountable government trying to raise money by any means possible isn’t to ban all technology created after the year 2000. The solution is to fix the government.

    1. …and it doesn’t make sense to me.  Ideally, we’d like to “fix government”, but government is not some kind of problem you can fix.  It consists of people, people who make good decisions and people who make very bad ones.  To date, have we “fixed government”, ever?

      Technology isn’t the answer to every problem.  It reminds me of the person who had no problem having the law enforcement look through their windows, monitor their backyard, capture their images on cctv networks, monitor their financial and transaction history, and have a backup of every electronic correspondence ever sent, because after all, they don’t have anything to hide, right?

      Having a free society carries some pretty heavy risks, as we have found out, and the civilian police in the US have already outfitted themselves for WWIII thanks to federal grants since 9/11.  Do we need to be constantly surveyed to catch some people with parking tickets or someone who got their Acura stolen?  No thanks, you can have it.

  5. Um, isn’t the issue here the laws, rather than the tech used to facilitate enforcement of said laws? Taking for granted for a moment that towing a car after 5 parking violations is a bad thing, indicting the APLR tech is just a distraction from the laws themselves.

  6. I’ve long wondered why license plates don’t also have bar codes on them. But while that could still be good for, say, parking police, who could walk around with a handheld scanner and record violations, you can’t really drive down the road with a swath scanner firing off pulses into people’s eyes and such.

    They’ve been doing this sort of thing in Portland, OR for a while now, too. 

    1. Mexican license plates have bar codes on them. The bar codes are rather small so I’m guessing they’re read with a hand held device for recording things like parking violations rather than the type of continuous scan mentioned in the post.

  7. This is really cool tech! If it can work at night, or at least with lights. Then a police force can drive through every street during the night and find stolen cars parked in plain view.

  8. I wonder how accurate the license plate recognition is.  What is the error rate?  I’m also surprised that the system ignores the color of the car.  I’d think that would be an important datum.

    1. Error Rate: massive. I’ve designed and trained on the deployment of these types of systems in the past, and they work beautifully in the lab, trade show floor, and in absolutely ideal conditions. If there’s nice sunlight, no fog, no rain, clean plate, no reflection (camera must be angled, not straight on), plate isn’t tilted more 10 degrees, it’s a local plate configured in the database and not from another state with a different font, the car isn’t effectively moving / swerving fast than the exposure time of the camera, etc., then the optical recognition can find the plate. 
      If you wanted to avoid detection from OCR, it’s incredibly easy to mess with your plate just enough to prevent a correct reading but not enough that it looks like you actually intentionally messed with your plate. 

      Plates in pretty much every country but the U.S. are far easier to read. California alone has like 50 different plate styles on the road. In the entire country of Germany I think there’s fewer, with comparatively little variation to boot. 

      1. I was a victim of whatever system the Harris County Toll Road Authority was using ten years ago. I suspect that it was people in an office keying numbers in from digital images. So I started getting one letter a week, each saying I had run a toll booth. The registration info they had on the citation matched car, but it didn’t match the picture. She was running booths at least three times a month. I got letters saying that I would have my car impounded.

        This was a hard problem to fix. I was driving around with an official from from a judge that I was not to be arrested on a warrant for twenty toll violations for about six months. The problem never cleared up until the other driver was dead. She ran off the road at high speed while she was drunk. I learned this from the clerk at the judge’s office handling my case.

  9. Jeeze, talk about distracted driving. He has his eyes on the road maybe 1/4th of the time he’s driving…

  10. One thing to keep an eye on is how long police depts keep the data, who has access to it and whether police depts are selling the info to insurance companies.

    1. Definately.  I don’t have a problem with the real-time scanning – I mean, that’s what licence plates are for, isn’t it; to be read?  But data retention and management?  Uh, no thanks.

  11. Police are already some of the shittiest drivers on road.  Jamming more distracting systems into patrol cars like this is bound to increase their accident rate.  Plus, I wonder how much it decreases actual cop effectiveness.  I.e. a big part of the value of a patrol car is noticing what is happening on the street, are some cars behaving strangely, does it look like a crime is in progress, etc.  A distraction like this is going to reduce their ability to notice what is going on around them.

    1. Here’s a revolutionary idea: Let’s ask some uniforms! Time for bb to host an actual LEO guest blogger, perhaps?

      1. Absolutely brilliant. And if by strange chance the Green Party candidate for Harris County (TX) Sheriff should win, I am sure he would be delighted to post here.

        Anyone know a cop who would want to post here?

      2. having been a cop for over 10 years and also having my law degree, i would love to answer questions sometime. of course i could not do it as a representative of my dept without prior permission.

        reading articles related to law enforcement and their associated comments, its always clear to me that most people have a very skewed idea of what being a cop is like. people also have crazy notions of how cops should police (such as shooting someone in the arm to disarm them, etc.). sadly most cops are victims of those few officers who do the wrong thing like the cannibal cop or rapist cop who lead most people to believe that all cops are bad.  cops are just like other people working other jobs, you have good cops, bad cops, laidback cops, and douchebag cops.

        as for the alpr system, my dept has it. funny enough, you are less distracted using it than not as the system automatically runs the tags versus me having to manually type the tags into my computer to check them on the state database while driving.

        further, most policing really is reactionary. people who think cops mostly drive around and discover crime are woefully misinformed. you really have to be lucky and be in the right place at the right time to roll up on a burglar, etc.

        and finally, many people scoff at police using vehicle pullovers as a good crime fighting tool. the number of times ive been told that i should be out “catching the real criminals” and not pulling cars over is too high to keep track of. my response to those comments is usually that the oklahoma city bomber was caught on a pullover for a broken taillight and ted bundy was caught for a traffic violation. pulling cars over for traffic violations gets cops in contact with vastly more people who may be wanted for serious crimes than any other technique. you also get contact with people who may not live in the immediate area and thus who you may not normally have contact with. you never know who is around you. i responded to a a suspicious person call on a quiet average looking hispanic guy. turns out he had beaten an elderly woman to death with a baseball bat in texas.

        if your local police dept has a ride along program or a citizens police academy program i would strongly suggest giving them a try. a change of perspective can do wonders for understanding.

        1. sadly most cops are victims of those few officers who do the wrong thing like the cannibal cop or rapist cop who lead most people to believe that all cops are bad.

          How many times have you reported a fellow officer for doing something wrong? Because, if you’re covering up their crimes, you’re a criminal as well.

          1. being a supervisor, i actually have to deal with that somewhat regularly, although its usually minor things not violations of law or violating people’s rights. i believe very much in the idea that if i stay quiet about a problem then im condoning it so yes, even prior to becoming a supervisor, i stepped up numerous times to report officer wrongdoing.  as a matter of fact, i basically drove my career straight into an iceburg when i first started as a cop at a different agency by stepping up about a precinct commander sexually harassing female officers. i had been a cop for mere months and he was a high ranking supervisor of several decades. my career there got tanked and i was called every name under the sun and had to leave to find work with another department after having no opportunities for advancement, but he got to resign instead of being fired and now works in a high powered state law enforcement job. of course it took three more women coming forward months after my complaint for anything to happen to him.

            the point i was trying to make originally is that due to the nature of our job, cops get lots of media coverage and typically that coverage is bad. if all anyone ever sees is cannibal and rapist cops people start to think thats all there is. police work is like other jobs, you have a spectrum of good people and bad. a majority of cops are just people trying to make a living. further, the job has been changing quite a bit from the cowboy years of the 70s, 80s, and 90s. theres a lot more professionalism in the job and a lot less tolerance of shenanigans. this doesnt mean of course that there arent huge problems in policing. it seems that nypd just cant get its shit together after an extensive history of issues. but theres also more guys like adrian schoolcraft who stand up against corruption now.

            another thing you have to consider is that standing up and speaking out doesnt seem to be something most people are willing to do. i wont recount the numerous historical examples of vast quantities of people remaining silent and allowing atrocities to happen. especially in this day and age where being a “snitch” is condemned, it shouldnt be surprising that most people stay quiet about wrongdoing. considering i basically lost my very promising career at a large police agency and had to put my aspirations on the shelf for having done the right thing by standing up for those who were unable to stand up for themselves, does it surprise you that people are hesitant to speak out?

            with regard to cops, it has gotten to a point that many of us are tired of dealing with all the negative public perception. when you deal with a citizen and from jump they are rude and have a crappy attitude despite you being professional and even friendly, it gets old really quick. that phenomenon really is no different than people making assumptions based on race or gender, etc. people love to assume all cops are jerks who want to jam them up somehow and who revel in covering up rogue cops. they arent.

            one way many cops try to fight this is to be better examples of the profession and by doing the right thing. this includes stepping up and policing their fellow officers. these are people we have to work with and nobody wants to work with a criminal or a troublemaker because those people make our jobs more difficult in so many ways. as a supervisor i try to impart to my troops the need to speak up against things they believe are wrong. frankly i think people in general need to be encouraged to do this. sadly, cops being professional and doing the right thing isnt good for ratings and rarely gets news coverage. but thats the world we live in.

            after all this longwindedness, all im trying to say is dont forget that cops are just people. as you would with other people, judge them individually based on your interaction with them. stand up and speak out when a cop does something wrong, but dont assume we are all cut from the same cloth. the job is changing albeit slower than many would like.

            i would really encourage you to attend a citizens police academy type program or do some ride alongs with different sized agencies. people are always surprised what doing this job actually entails. of course if you are ever in georgia you are always welcome in my neck of the woods.

  12. Parking enforcement in my little burg now takes time stamped photos with four cameras that are roof mounted on their trucks, rather than chalking tires on cars in unmetered parking spots. Ticketing, now so much more efficient, has gone through the roof. I have always hated that parking enforcement fucker. Now I hate his truck, too.

  13. I <3 parking enforcement. Tow them all. If they park illegally, or even just park poorly, haul them away.

  14. As a pedestrian and bicyclist, I have no problem with technology that gets more cars off the road.

    Also, increased revenue from scofflaws means decreased tax burden for those that play by the rules.

  15. 24,000,000 reads in a county with only 9,889,056 people. I think that makes it pretty clear they have a database of the comings and goings of citizens who are not under investigation or suspected of a crime. Shouldn’t the ACLU be all over this?

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