LPR cameras and ANPR: how license plate recognition works and what to check

ANPR is the usual name in the UK, India and Australia. In the US you will mostly see license plate recognition, LPR, or ALPR for automatic license plate recognition. A camera maker's guide lists still more names for the same thing, including automatic vehicle identification.

So an ANPR camera, an LPR camera, a license plate recognition camera and a license plate reader camera are all the same kind of product. A camera sold for plates is also called a license plate capture camera. This guide uses the names ANPR and LPR.

An ANPR system has three parts: the camera, the software and what happens to the result. The camera sets the limit for the other two. One camera maker puts it plainly: no algorithm, however sophisticated, can read a plate that is not clearly visible in the image.

• The camera captures a clear picture of the plate.
• Software finds the plate in the picture and reads the letters and digits. It can run on the camera or on a computer.
• The result is stored in a database or used to trigger an action, such as opening a gate or sending an alert.

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Camera makers list access control, parking management and tolling on fast roads. On a business site the common uses are simpler.

• A log of vehicles at the gate, yard or dock, with the time.
• A list of plates you expect, so an unknown vehicle gets noticed.
• Looking back when a delivery, a dispute or a theft needs a date and a plate.
• Opening a barrier for plates on an approved list.

Plate reading is a camera job first. Two camera makers' installation guides agree on most of the points below, and the numbers come from them. Treat them as a starting point. Your camera's own manual comes first, and so does a test at your gate, by day and at night.

• Angle. Keep the angle between the camera and the way vehicles travel under 30 degrees, sideways and up and down, so the plate is seen close to head on. One maker adds that the software will not work reliably beyond its stated angle limits, so ask for them.
• Height. Mount the camera above headlight level. Lights shining straight into the lens can blind it. Keep it away from street lamps and other strong lights.
• Distance and speed. Faster vehicles need a longer view, or the software has no time to read the plate before the vehicle leaves the picture. One maker suggests at least about 4 metres between camera and vehicle at 10 km/h, 7 metres at 30 km/h and 11 metres at 50 km/h, for software that checks five pictures a second.
• Size of the plate in the picture. For a standard European plate, one maker says at least 74 pixels across the width are needed to make out the characters, and most reading software wants about 100 to 150. Plates differ by country. A maker's guide says Middle Eastern plates need more pixels than Western European ones.
• Resolution. For European plates, one maker says 1 megapixel covers one lane up to 4 metres wide and 2 megapixels covers two lanes up to 8 metres wide. More is not always better, because very large pictures slow the software down.
• Light at night. Plates are made of material that reflects light straight back to its source, so infrared light works well when it sits right next to the camera. Light fades fast with distance: doubling the distance needs about four times the infrared power to keep the plate as bright.
• Shutter time. A short shutter stops motion blur. One maker suggests about 1/500 of a second for vehicles that slow or stop, and 1/1750 to 1/2500 for traffic at 120 km/h. Another gives about 1/100 of a second at a 10 degree angle and 30 km/h, and about 1/500 at a 30 degree angle and 50 km/h. Ordinary camera settings often use about 1/30, which blurs a moving plate.
• Wide dynamic range. One maker says to switch it off for plates unless the camera's specification says otherwise, because it can cause odd artifacts on moving vehicles.
• Plate camera or ordinary camera. A camera made for plates comes with settings chosen for the job and saves time. An ordinary camera can work if you place, light and set it up for plates.

In the US, ANPR is called license plate recognition, LPR, or ALPR. An LPR camera, a license plate recognition camera and a license plate reader camera are the same idea: a camera that sees the plate, and software that reads it into text. Many systems also keep a wide picture of the vehicle next to a close crop of the plate.

A US plate is 12 inches wide and 6 inches tall, about 30 by 15 cm. A standard European plate is about 52 cm wide. The pixel figures earlier in this guide are for a European plate, and one camera maker notes that smaller plates might need a higher resolution. At the same distance, a narrower plate gets fewer pixels across. Plates also differ from state to state, with their own colours, logos and number formats.

Rules on reading plates depend on your state and city, so ask a lawyer before you start. We read Indian number plates today and not US ones, so this section is here to help you choose a camera and a supplier. When you compare cameras and software, check these.

• Distance. Makers give different working ranges for their plate cameras. One maker's kit for gates and barriers works at 7 to 23 feet (2 to 7 metres) from a mount up to 10 feet (3 metres) high. Its kit for traffic driving past works at 23 to 65 feet (7 to 20 metres) from a mount 10 to 33 feet (3 to 10 metres) high. Another maker says most LPR systems work best at 15 to 35 feet from the plate. Read your own camera's datasheet.
• Angle. Keep it under 30 degrees, sideways and up and down. One maker suggests a capture distance of about twice the mounting height.
• Shutter. Plate cameras use short shutter times. One maker lists 1/1000 of a second or faster as a key spec for an LPR camera. A camera left on default settings often blurs a moving plate.
• Light at night. Look for infrared light that sits right next to the camera, because plates reflect light straight back to where it came from.
• Pixels on the plate. Ask the supplier to show a real picture from your site and measure the plate. One maker's plate software asks for a plate at least 130 pixels wide for a plate with one row of characters, and 70 pixels for two rows.
• Plates it reads. Ask about plates from your state, from other states and from special plate types. Ask to see it read yours.
• Storage. What is kept, for how long, who can see it, and can entries be deleted?
• A test. Ask to see it working at a site like yours, by day and at night, before you sign.

Most failures come from the picture, not the software. We do not quote accuracy figures in this guide. A supplier's figure depends on how it was tested, so ask to see the system working at your gate.

• Blur. The shutter is too slow, or the vehicle too fast for the view.
• Glare. Headlights or a bright lamp in the shot, or a camera mounted too low.
• Too few pixels. The camera is zoomed out to cover the whole yard, so the plate is tiny.
• A sharp angle. The camera sits to one side or high above, so the characters look squashed.
• Dirty, bent, faded or covered plates.
• Bad weather. One maker says rain, snow and fog can severely limit what the camera sees at long distances.
• Plates the software does not support. Each product supports a list of countries and plate types.

A number plate can lead to a person, so plate records are often treated as personal data. Rules differ by country. This is a short guide, not legal advice, so ask your own adviser what applies to your site.

• UK: the ICO says a number plate is personal data when you collect it as part of a surveillance system to identify an individual. Its ANPR checklist asks for a real need to read plates, a data protection impact assessment, as few ANPR cameras as you can, clear and prominent signs, and a retention and disposal policy. The ICO says the guidance is under review because of the Data (Use and Access) Act, so check its page for the latest.
• US: the rules sit mostly with the states. The National Conference of State Legislatures counts at least 28 states with laws on the use of plate readers or on keeping the data. Most of those laws are written around police use, and the retention limits in state laws range from three minutes in New Hampshire to five years in Alabama. Check your own state before you start.
• India: the Digital Personal Data Protection Act, 2023 covers digital data about an identifiable person. It asks the business that decides why the data is collected to protect it and to erase it once its purpose is served, unless the law says to keep it. The Rules were notified on 14 November 2025 and are phased in over 18 months.
• Whatever the country, the habits are the same: have a real reason to read plates, use as few cameras as you need, put up clear signs, keep the data only as long as you need it, and limit who can see it.

Brochures rarely say what happens at a muddy gate at night. These questions get you answers that matter.

• Which countries and plate types does the software read? Ask to see it read yours.
• What does the camera need at my gate: angle, height, distance, light? Can you show it on a real site, by day and at night?
• What is stored: plate text, time, a photo, a video clip? Where, and for how long?
• Who can see the log, and can I delete entries?
• What happens when the software misreads a plate or cannot read it?
• Does it need a dedicated camera, or can it use the one I have?
• Can it keep a list of expected plates and warn me about others?
• What do I need to put on my signs and in my paperwork?

We set up number-plate reading on the gate camera you already have. It is set up for your site, not on by default, because angle, light and the way vehicles approach are different at every gate.

Each plate we read goes into a log with the time, the camera and a photo, kept for 30 days. You can give us a list of plates you expect. A plate on the list is logged quietly. A plate that is not on it sends a warning with the photo to your Telegram.

Today we read Indian number plates in the standard format. We do not read UK or US plates, so we will not set it up for them. Our software installs in 60 seconds on a computer at your site, and fire and smoke, after-hours intrusion and camera tampering run from the start. Our ANPR camera page has the details.