License Plate Reader Security Cameras (known as Automatic Number Plate Recognition in Europe) are an excellent way to add extra security to your facility, letting you capture and keep a record of any vehicles entering and exiting the premises. But how do they work, and what kind of camera setup do you need to run license plate readers?
When it comes to reading license plates, you essentially have two options: Installing dedicated license plate readers, or simply opting for high-definition IP cameras with enough resolution to capture and read license plates clearly.
IP Security Cameras for License Plate Reading
The easiest way to read license plates actually does not require any special software or hardware, utilizing nothing more than IP security cameras with enough resolution to clearly make out the license plate when zoomed in. To achieve this, a camera must have an adequate number of Pixels Per Foot (PFF) and a proper horizontal field of view. A PFF of 40 or above is often regarded as a good rule of thumb, but this number is often arbitrary and depends on a number of factors. Many security camera installers recommend 50-60 PFF, if you’re looking to achieve clarity and quality without a margin of error.
Generally, the minimum resolution necessary for reading license plates is 1080p. 720p or below is usually not enough to achieve a clear image. Even higher resolutions, such as 1440p or 4k UHD will be an even better option, providing much larger, clearer images that can be enlarged without a large loss in clarity.
But high resolution alone is not enough to properly capture license plates. Security cameras must be placed strategically, at the proper angles, and installed professionally, to clearly capture license plate numbers. Cameras placed at too high an angle will not be able to see the plate, while cameras placed too far away will not be able to zoom in properly.
The number you should be looking for is Horizontal Field of View – the width of the image the camera captures. For example, using a 6mm lens placed 40 feet away from the car’s passing point will give you a horizontal field of view of 24 feet.
Lighting is also important, as license plates are generally hard to read at night without proper flash and anti-glare cameras. A slight increase in resolution may be necessary to compensate for a loss in contrast or poor illumination. And since headlights can cause significant glare, it is usually easier to place cameras to capture rear plates as opposed to those on the front of the car, where headlights may blind the camera.
License Plate Reader (LPR) Camera Systems
Dedicated LPR camera systems are high-tech systems that use a combination of high-definition cameras and special optical character recognition (OCR) to capture and identify license plates. The image is then sent to the LPR camera software, which interprets the letters and numbers on the license plate and then compares them to a database or list of license plate, many of which are flagged if of interest.
Law enforcement often uses systems like this to track and locate vehicles of interest, but businesses and properties can also use them for keeping track of who enters or exits the premises. Allowed vehicles and VIPS can be checked and verified as they enter the premises, and unwanted or banned vehicles can be stopped before they attempt to enter. Administrators can create and modify the list of allowed or banned vehicles as they see fit and be alerted immediately of any flagged vehicle entering the property.
Commercial grade, dedicated security cameras with license plate readers usually come with their own proprietary OCR software. If you’re looking to use regular HD or UHD IP cameras to capture license plates, there are software available for purchase, as well as open source programs that can help.
Privacy Concerns Regarding License Plate Reader Cameras
Some people may be concerned about invasion of privacy when reading license plate numbers. However, as they are displayed on the outside of the vehicle on public roadways, license plates are usually considered in most jurisdictions to be public information that may be captured on video or film – without notice posted or consent from the owner or driver of the vehicle. The private information usually associated with license plates – registration details, addresses, names – is only available to law enforcement.
Choosing the Right LPR Camera
Day Time vs Night Time License Plate Reader
The accuracy of a license plate security camera can be compromised if lighting conditions are not right, or if cameras are not properly equipped to record in low lighting and glaring light. Reading license plates at night is especially a challenge, as images will be too dark to make anything out without adequate lighting. There are a few solutions to this, including buying license plate cameras with WDR and IR capabilities.
WDR License Plate Reader Camera
License plate reader cameras with WDR (Wide Dynamic Range) provide clear, even images in areas with contrasting light. WDR cameras determine the correct exposure for the image in real-time, to produce a balanced image that is properly illuminated. This lets WDR license plate cameras record clear footage in situations where street lamps, headlights, and other light sources would otherwise obscure the image.
IR Plate Reader Camera
IR (infrared) night vision is a common way to clearly capture license plates in the dark. IR license plate cameras are often used by police to monitor traffic. Infrared cameras use LED lights in the front of the camera to illuminate areas with infrared light, which is invisible to humans. The infrared light allows cameras to capture illuminated, monochrome images of the area. Security cameras with an IR cut filter will adjust IR light levels depending on whether it’s day or night, to provide consistent colored images.
License Plate Security Camera Lens
A plate reader camera with a varifocal lens lets you adjust the angle, focal length, and zoom of the camera to capture different areas in detail. This is helpful when you have a specific area or access point you want to focus on, or if you want to monitor different areas of your parking facility with the same camera. Many network cameras with varifocal lenses allow users to adjust the lens directly from the NVR platform, instead of doing it manually.
License Plate Recognition Camera vs License Plate Capture Camera
A license plate recognition camera and a license plate capture camera may sound like exactly the same thing, but there are key differences. License plate capture cameras operate similarly to basic security cameras, only with higher resolution, shutter speed, and headlight compensation to capture license plate numbers in a variety of conditions. License plate recognition cameras, such as the Flock license plate reader, combine special optical character recognition and license plate reader software to actually read plate numbers, then store them in a database using a VMS.
LPR Camera Vantage Point
When mounting a license plate reader camera, it is important to consider the camera angle, location, and distance from the vehicles. Cameras should be ideally be installed exactly flush with the license plate, but any vertical angle less than 30 degrees should be adequate to read plate numbers. Horizontal angles should be less than 15 degrees. Mount your cameras at too high an angle, and the plate numbers may be too slanted to read, or be blocked by bumpers on SUVs and trucks. The closer cameras are placed to the vehicle, the better, though cameras with higher zoom may not require close placement.
License Plate Reader Vehicle Speed
How fast will the cars in your area be moving? The slower vehicles are moving, the better your camera will be able to clearly capture plate numbers. A vehicle that is moving under 5 MPH within 20 feet of the camera will be easy to read for most license plate cameras in various weather and lighting conditions. More advanced license plate reader cameras with higher frame rates will be able to capture faster-moving vehicles. For example, Digital Watchdog license plate readers can record license plate numbers at up to 50 MPH, and Hikvision license plate cameras can work at up to 75 MPH.
License Plate Security Camera for Car Make and Model
A license plate reader security camera should be zoomed in on license plates as much as possible to capture clear and readable images. If you also want to capture the make and model of vehicles in your property, a good option is to use a dual sensor license plate camera, or to install another CCTV camera in the area with a wider view. In a dual sensor LPR camera, one sensor captures a narrow view of license plates, while another sensor captures a wider view of your area. This lets you see the make and model of cars without sacrificing clear license plate images. Many cutting-edge LPR security cameras offer intelligent video analytics, letting you search past footage for specific car makes, models, colors, and plate numbers. Another option is to install a separate security camera to survey the wider area.
Do You Want to White List and Black List License Plates?
Advanced license plate recognition cameras can scan the plate number of each vehicle that enters your property, and store it in a database. This lets you white list and watch list certain license plates. If someone commits a crime on your property, you can watch-list their license plate, and an alarm will be sounded and/or a security alert will be sent any time they enter your property again.
License Plate Reader Software
To catalogue license plate numbers, you will probably need a video storage device such as a DVR or NVR, as well as license plate reader software that can work with your security system to compile a database. Milestone XProtect is a great example of security software that can support compiling, white listing, and watch listing vehicles, as well as searching through stored footage for specific cars. Many LPR cameras also combine with micro SD cards, which store images from your security cameras so they can be transferred to a computer.
License Plate Cameras That Catalogue Plates
Some cameras simply record license plates so you can view them in footage, while others transfer all license plate numbers into a database, letting you easily see a list of all license plates that have entered your property, and when. With automatic OCR number-plate recognition, all license plate numbers will be scanned and stored. This requires a true license plate recognition camera instead of a “capture” camera which takes clear images but does not actually scan and read plate numbers. LPR cameras that use software to store plate numbers allow you to search video footage for specific plates.
License Plate Reader Camera Budget
A dedicated LPR camera can cost anywhere from $300-$3,000, depending on the camera type, video quality, and range of features. Additional costs are required for NVRs and software licenses necessary to use the security platforms. Advanced cameras that offer intelligent video analytics, visitor management, vehicle watch listing, and similar features will generally cost more.
It is possible to capture the license plates of slow vehicles with a high-resolution CCTV camera that is not designed for license plate recognition. But without the proper resolution, settings, and camera placement, your camera will not be able to consistently provide clear images of license plates — especially at night. If you want to capture license plates at night, an LPR camera is necessary, as these have back lighting adjustments which allow it to record despite low lighting, the glare of headlights, and bad weather conditions. LPR cameras are designed to balance extreme light levels and capture high-speed vehicle license plates, providing clear and accurate plate numbers on a consistent basis.