ALPR / NPR Recognition Accuracy and Issues

By Carlton Purvis, Published on Jan 15, 2014

Sick of red light and speed cameras? A lot of people are. There are entire websites and web forums devoted to the public’s disdain for automated policing. But is there a way to beat them? Forget the aerosol sprays and chunky license plate covers [link no longer available]. In this post we show you, straight from a US government commissioned report, what things have been proven to give ALPR systems problems in reading plate numbers.

Because more and more law enforcement agencies are using automatic license plate recognition, the International Association of Chiefs of Police, with a grant from the National Institute of Justice was commissioned to asses ALPR implementation among U.S. agencies. It used results from 305 agencies across the U.S. including one of the biggest ALPR users, the Washington, D.C. Metropolitan Police Department [link no longer available]. The final report is where this data comes from.

The most common types of ALPR being used by U.S. agencies is mobile. Ninety-five percent of respondents said they used mobile APLR, while under 20% use fixed or portable.

However, mobile has the lowest capture and read rate of the three, according to the report.

ALPR Issues

Beating ALPR is much more simple than spending money on an infomercial product. Here are the three main things highlighted in the report:

Dirty or Bent Plates

Because ALPR systems often rely on reflectivity, plates that are bent, dirty or damaged “may cause the ALPR software to misidentify a character.”

Physical Obstructions

Bike racks, tow hitches and town bars are common physical obstructions that can lead to a misidentified license plate. A repo man from Maryland I spoke to said tow hitches are something they have a problem with, and they suspect some SUV owners have them just for this purpose.

The report provided these examples of unreadable plates:


Reddish Tones

“Some colors, especially reddish tones, may be difficult for ALPR system[s] to read,” the study says. It doesn’t say why but it does say plate design has a major impact on how well an ALPR system is going to read a plate. Not only to plate designs vary from state to state and within a state, the shape of the characters also vary.

Number Design

Other things that can impact the accuracy of a read are whether the numbers are raised or not, the report says, but it doesn't indicate whether that is better or worse for determining plate numbers. Some systems aren't configured to read plates from other states. The report does not identify which those are.

Capture and Read Rates

Data on U.S. ALPR capture and read rates is hard to find, but these are the lowest acceptable performance rates for Europe's Schengen member states:

U.S. law enforcement say despite the problems mentioned earlier, ALPR still increases their productivity. Two anecdotes from the study:

  • "Montgomery County (MD) Police Department, for example, has indicated that a single officer equipped with ALPR scanned 48,101 plates, resulting in the issuance of 255 traffic citations, the identification of 26 drivers with suspended licenses, 16 vehicle emission violators, 4 stolen and 1 expired license plate tags, and 3 arrests in the course of 96 hours of use over 27 days."
  • In five days of scanning at the U.S. Mexico border law enforcement scanned 780,000 plates and “over 1,300 were involved in 4 murders, 14 rapes, 24 robberies, 273 assaults, 128 burglaries, 345 vehicle thefts, 361 weapons, and 241 narcotics cases.”

ALPR Uses?

Ninety-five percent of the agencies using ALPR used it mainly for auto theft. Most (68 percent) reported an increase in vehicle recoveries and arrests in auto theft cases after adopting ALPR. And other less common uses like toll enforcement, speed and stop light enforcement and calculating traffic flow.


Are a Lot of Agencies Using ALPR?

The number of agencies using ALPR is growing steadily every year. Of the 305 agencies surveyed by the IACP, 70 (23%) said they used ALPR. A similar survey from 2011 found that larger agencies were adopting the technology at a faster rate. Of these larger agencies (10,000 or more officers), 71 percent use ALPR.

Do Most Agencies Have Policies For ALPR Use?

Most do not. Only 48 percent actually had any written policies for ALPR use.

How Long Is ALPR Data Stored?

Around 40 percent of the agencies surveyed store the data for six months, 13 percent store it indefinitely. Nearly half (43 percent) updated their “hot lists” daily.

Comments (3) : Members only. Login. or Join.

Related Reports

The US Fight Over Facial Recognition Explained on Jul 08, 2020
The controversy around facial recognition has grown significantly in 2020,...
Clearview AI Alarm - NY Times Report Says "Might End Privacy" on Jan 20, 2020
Over the weekend, the NY Times released a report titled "The Secretive...
Integrated IR Camera Shootout 2020 - Avigilon, Axis, Bosch, Dahua, Hanwha, Hikvision, Panasonic, Uniview, Vivotek on Jan 30, 2020
The best and worst cameras tested in this IPVM shootout showed major...
Latest London Police Facial Recognition Suffers Serious Issues on Feb 24, 2020
On February 20, IPVM visited another live face rec deployment by London...
Masks Cause Major Facial Recognition Problems on Feb 24, 2020
Coronavirus is spurring an increase in the use of medical masks, which new...
Facial Recognition: Weak Sales, Anti Regulation, No Favorite, Says Security Integrators on Jul 07, 2020
While facial recognition has gained greater prominence, a new IPVM study of...
Fever Camera Sales From Integrators Surveyed on Jun 01, 2020
Fever cameras are the hottest trend in video surveillance currently but how...
Axis Compares Fever Camera Sellers to 9/11 on Sep 18, 2020
Axis Communications, the West's largest surveillance camera manufacturer, has...
Amazon, Microsoft and IBM Abandoning Face Recognition Is An "Irresponsible PR Stunt" Says AnyVision on Jul 17, 2020
In the wake of national protests against US police abuses, big tech firms...
Face Masks Increase Face Recognition Errors Says NIST on Aug 04, 2020
COVID-19 has led to widespread facemask use, which as IPVM testing has shown...
Worst Over But Integrators Still Dealing With Coronavirus Problems (June Statistics) on Jun 30, 2020
While numbers of integrators very impacted by Coronavirus continue to drop,...
Bias In Facial Recognition Varies By Country, NIST Report Shows on Jul 15, 2020
While many argue that face recognition is inherently racist, results from one...
Terrible Convergint Coronavirus Thermal Camera Recommendation on Apr 01, 2020
A week after Convergint disclosed falling revenue, pay and job cuts,...
Video Analytics 101 on Mar 16, 2020
This guide teaches the fundamentals of video surveillance...
London Live Police Face Recognition Visited on Feb 13, 2020
London police have officially begun using live facial recognition in select...

Recent Reports

Panasonic Presents i-PRO Cameras and Video Analytics on Oct 19, 2020
Panasonic presented its i-PRO X-Series cameras and AI video analytics at the...
Augmented Reality (AR) Cameras From Hikvision and Dahua Examined on Oct 19, 2020
Hikvision, Dahua, and other China companies are marketing augmented reality...
18 TB Video Surveillance Drives (WD and Seagate) on Oct 19, 2020
Both Seagate and Western Digital recently announced 18TB hard drives...
Watrix Gait Recognition Profile on Oct 16, 2020
Watrix is the world's only gait recognition surveillance provider IPVM has...
Intel Presents Edge-to-Cloud Ecosystem for Video Analytics on Oct 16, 2020
Intel presented its processors and software toolkit for computer vision at...
Best Manufacturer Technical Support 2020 on Oct 16, 2020
5 manufacturers stood out as providing the best technical support to ~200...
Microsoft Azure Presents Live Video Analytics on Oct 15, 2020
Microsoft Azure presented its Live Video Analytics offering at the September...
Worst Manufacturer Technical Support 2020 on Oct 15, 2020
4 manufacturers stood out as providing the worst technical support to ~200...
Clorox Announces, Then Pulls, Fever Camera on Oct 15, 2020
For almost one week, Clorox was marketing fever cameras. The booming...
Faulty Hikvision Fever Cam Setup at Mexico City Basilica and Cathedral on Oct 14, 2020
Donated Hikvision fever cameras (claiming screening of 1,800 people/min. with...
Directory of 209 "Fever" Camera Suppliers on Oct 14, 2020
This directory provides a list of "Fever" scanning thermal camera providers...
Avigilon UMD / UAD Tested on Oct 14, 2020
Avigilon's Unusual Activity Detection and Unusual Motion Detection claim to...
Longse Promoting Hikvision Partner Fullhan Chip Based Cameras on Oct 14, 2020
With Huawei HiSilicon production being shut down at TSMC, camera...
Meridian & Goodview (BEMS Relabeller) Temperature Screening Tested on Oct 13, 2020
A lot of temperature tablets look exactly alike and that is because they use...
Monitoring Alarm Systems From Home - Innovation or Danger? on Oct 13, 2020
Remote monitoring by alarm companies since COVID-19 is bringing cost savings...