License Plate Readers For Security Cameras
License Plate Recognition 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 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 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.
Dedicated LPR 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 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 Readers
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.