API Documentations - LPR API

API Documentation

LPR (License Plate Recognition) API 2.0 (Coding Examples)

Our LPR API can be deployed in two primary ways: either the entire process is performed on-site in real-time, or images from multiple locations are transmitted to a central location where the LPR/OCR process is conducted later via our LPR API. When processed on-site, the captured plate information—including alphanumeric data, date-time, location identification, and any other required details—is completed and can be transmitted to remote computers for further processing or stored locally for later retrieval.

Please note that the output from this service may require additional verification due to potential complications during the recognition and translation process.

To achieve the highest possible recognition speed, image size is a critical factor.

Avoid Submitting The Same Image More Than Once

Our system deducts one credit from your account balance for each XML or JSON result returned, regardless of the outcome. Therefore, please ensure your system has a mechanism in place to prevent sending the same image to the API service more than once.

REST API Description

This API uses multipart POST HTTP method. Ensure HTTP POST is a multipart/form-data request. The following three parameters and their values are required.

Parameter Name	Parameter	Value	Used in URL
API Key	accesscode	xxxxx-xxxxx-xxxxx-xxxxx	POST https://lpr.recognition.ws/v2?acccesscode=xxxxx-xxxxx-xxxxx-xxxxx&saveimage=TRUE
Input Image*	Image File*	JPG, JPEG, PNG, GIF, BMP	POST https://lpr.recognition.ws/v2?acccesscode=xxxxx-xxxxx-xxxxx-xxxxx&saveimage=TRUE
Save Image**	saveimage**	TRUE or FALSE (default: FALSE)	POST https://lpr.recognition.ws/v2?acccesscode=xxxxx-xxxxx-xxxxx-xxxxx&saveimage=TRUE
Data Format***	format***	XML or JSON (default: XML)	POST https://lpr.recognition.ws/v2?acccesscode=xxxxx-xxxxx-xxxxx-xxxxx&saveimage=TRUE&format=JSON

* Only one image file is allowed in a POST request. A POST request with multiple files would be rejected immediately. Only the first found license plate will be processed if an input image contains more than one license plate.

** Set parameter "saveimage" to "TRUE" if you'd like our system to save the input image so that later you can log in to your account to review it. Set the value of this parameter to "FALSE" otherwise.

*** Set parameter "format" to "JSON" if you'd like the service to send data in Json format. If you don't include this parameter at all in the API URL, or explicitly set the value of this parameter to "XML" to get data in XML format.

                    
    <html>
       <form enctype="multipart/form-data" action="https://lpr.recognition.ws/v2?accesscode=xxxxx-xxxxx-xxxxx-xxxxxx&saveimage=FALSE" method="POST">
          Choose an image to process: <input name="anyName" type="file" />
          <input type="submit" value="Go" />
       </form>
    </html>

Input Image Specs

Standard license plate characters have to meet the specification of at least 25 pixels high characters. In general, OCR can decode characters lower than this requirement but not at the extremely high(99.8%) accuracies required.

From an APR/OCR perspective, resolution well above the 25-pixel requirement does not significantly translate into better performance but can lead to significantly increase real-time execution due to larger image sizes. To mitigate this, incoming images are typically resized such that the nominal plate character height is in a range of 25-35 pixels high. This creates a problem for motorcycle images since the resizing appropriate for passenger cars and trucks causes motorcycle plate characters to fall well below the 25-pixel requirement. The vehicle type input into ALPR would allow the algorithm to dynamically adjust the resizing, based on the known vehicle type, in order to capture motorcycle plates accurately. As it stands today, motorcycle plates are typically missed completely or recognized with much higher error rates.

More often than not, the "jurisdiction" characters are much smaller than the plate characters.

Input Image Specs	Without Reading Region/Country	To Read Region/Country
Height of the License Number portion in a License Plate	20 - 150 pixels	100 - 750 pixels
Width of the License Number portion in a License Plate	80 - 400 pixels	80 - 400 pixels
Length of License Number	4 - 10 characters	4 - 10 characters
Size of Input Image	< 2.0 MB	< 2.0 MB

Output in XML or Json

License Number: Plate number in ASCII
Region: USA State or Canadian Province
Country: Canada or USA
Position of the License Number portion in an input image: Top(pixels), Left(pixels), Width(pixels), Height(pixels). The origin(0,0) is the top-left corner of an input image.

            

    // XML

    <?xml version="1.0" encoding="UTF-8" standalone="true"?>
    <LPR Version="2.0" Date="4/22/2015" Status="SUCCESS">
      <License_Number>ABCD-1234</License_Number>
      <Region>New York</Region>
      <Country>USA</Country>
      <Confidence>0.915</Confidence>
      <Left>279</Left>
      <Top>357</Top>
      <Width>243</Width>
      <Height>69</Height>
    </LPR>

            

    //Json

    {
      "service": "lpr",
      "version": "2.0",
      "date": "3/8/2021 11:07:21 PM",
      "status": SUCCESS,
      "license_number": "ABCD-1234",
      "region": "New York",
      "country": "USA",
      "confidence": 0.915,
      "left": 279.0,
      "top": 357.0,
      "width": 243.0,
      "height": 69.0
    }

Error Codes

Error Code (Key)	Description (Value)
0	Database Errors.
23	Insufficient balance for Recognition.
25	No image has been uploaded.
26	Recognition failed.
27	Unknown error(s) occured.
29	One or more required parameters missing.

                    

    // XML

    <?xml version="1.0" encoding="utf-8" standalone="yes"?>
    <LPR version="2.0" Date="5/28/2015 1:39:10 PM" Status="FAILED">
      <Message Key="0" Value="Database Errors." />
    </LPR>

                
    {
      "service": "lpr",
      "version": "2.0",
      "date": "03/08/21 3:23:27 PM",
      "status": "FAILED",
      "message_key": 0,
      "message": "Database Errors." 
    }

Coding Examples (XML and Json)

JavaScript(Python, C#, Java, Swift)



    <html>
    <head></head>
    <body>
    <form id = "form">
        <label>Please submit an image containing a license number:<input type = "file" id = "input"></label>
        <br>
        <a href="javascript: fetchResponseXml()"> Submit (XML Output) </a>
        <br>
        <a href="javascript: fetchResponseJson()"> Submit (Json Output) </a>
    </form>

    <pre id = "p1"></pre>
    </body>

    <script>

    const form = document.getElementById("form")
    const out = document.getElementById("p1")


    // JavaScript XML

    async function fetchResponseXml() {
        console.log("XML")
        const url = "https://lpr.recognition.ws/v2?accesscode=YOUR_ACCESS_CODE"
        var imgInput = document.getElementById("input")
        var img = imgInput.files[0]
        var formData = new FormData();
        formData.append('file', img)

        var parser = new DOMParser();
        var xmlHttp = new XMLHttpRequest();
        xmlHttp.open("POST", url, false);
        xmlHttp.send(formData);
        var xmlResponse = parser.parseFromString(xmlHttp.responseText, "text/xml");
        var text = "";
        var children = xmlResponse.documentElement.children;
        for (var i = 0; i < children.length; i++) {
            text += children[i].nodeName + ": " + children[i].textContent + "\n"
        }

        out.textContent = text;
    }

    // JavaScript Json

    async function fetchResponseJson() {
        console.log("JSON")
        const url = "https://lpr.recognition.ws/v2?accesscode=YOUR_ACCESS_CODE&format=JSON"

        var imgInput = document.getElementById("input")
        var img = imgInput.files[0]
        var formData = new FormData();
        formData.append('file', img)

        var xHttp = new XMLHttpRequest();
        xHttp.open("POST", url, false);
        xHttp.send(formData);
        var jsonResponse = JSON.parse(xHttp.responseText)
        var text = "";

        for (let childProperty in jsonResponse) {
            let childValue = jsonResponse[childProperty];

            if (typeof childValue === 'object') {
                text += childProperty + ": \n" 
                for (let nestedChildProperty in childValue) {
                    let nestedChildValue = childValue[nestedChildProperty]
                    text += "\t" + nestedChildProperty + ": " + nestedChildValue + "\n";
                }
            } else {
                text += childProperty + ": " + childValue + "\n";
            }
        }

        out.textContent = text;
    }

    </script>
    </html>

Python(JavaScript, C#, Java, Swift)



    ### Python XML

    import xml.etree.ElementTree as ET
    import requests

    url = "https://lpr.recognition.ws/v2?accesscode=YOUR_ACCESS_CODE"
    path = "YOUR_IMAGE_PATH"

    with open(path, 'rb') as img:
        imgName = os.path.basename(path)
        images = {'image': (imgName, img)}
        with requests.Session() as s:
            r = s.post(url, files = images)
            xml = ET.fromstring(r.text)
            output = "License Number: " + xml[0].text
            print(output)

    ### Python Json

    import requests
    import json
    import os

    url = "https://lpr.recognition.ws/v2?accesscode=YOUR_ACCESS_CODE&format=JSON"
    path = "YOUR_IMAGE_PATH"

    with open(path, 'rb') as img:
        imgName = os.path.basename(path)
        images = {'image': (imgName, img)}
        with requests.Session() as s:
            r = s.post(url, files = images)
            result = r.json()
            for attribute, value in result.items():
                print(attribute, ":", value)

C#(JavaScript, Python, Java, Swift)



    // C# XML

    using System;
    using System.IO;
    using System.Net;
    using System.Xml.Linq;


    static void Main(string[] args)
    {
        String url = "https://lpr.recognition.ws/v2?accesscode=YOUR_ACCESS_CODE";
        String imagePath = "YOUR_IMAGE_PATH";
        WebClient client = new WebClient();
        byte[] response = client.UploadFile(url, imagePath);
        String responseString = client.Encoding.GetString(response);
        XElement root = XElement.Parse(responseString);

        // Iterating for "License_Number" item in the root tag.
        var el = root.Elements("License_Number");
        Console.WriteLine("License Number: " + (string) el.Value);

        IEnumerable<XElement> test =
             from el in root.Elements("License_Number")
             where (string) el.Value != null
             select el;
         foreach (XElement el in test)
             Console.WriteLine("License Number: " + (string)el.Value);
    }

    // C# Json

    using System;
    using System.IO;
    using System.Net;
    using System.Net.Http;
    using System.Xml;
    using Newtonsoft.Json.Linq;

    static void Main(string[] args)
    {
        String url = "https://lpr.recognition.ws/v2?accesscode=YOUR_ACCESS_CODE&format=JSON";
        String imagePath = "YOUR_IMAGE_PATH";
        WebClient client = new WebClient();
        byte[] response = client.UploadFile(url, imagePath);
        String responseString = client.Encoding.UTF8.GetString(response);

        Console.WriteLine("\nJSON Output (Parsed): \n");

        JObject jsonResponse = JObject.Parse(responseString);

        foreach (var node in jsonResponse)
        {
            Console.WriteLine(node.Key + ": " + node.Value);
        }
    }

Java(JavaScript, Python, C#, Swift)



    // Java XML

    ...
    import java.net.HttpURLConnection;
    import java.net.URL;


    public static void main( String[] args )
    {
        URL url;
        String response = "";
        try {

            url = new URL("https://lpr.recognition.ws/v2?accesscode=YOUR_ACCESS_CODE");

            final HttpURLConnection con = (HttpURLConnection) url.openConnection();

            final String imagePath = "YOUR_IMAGE_PATH";
            postImage(con, imagePath);

            BufferedReader br = new BufferedReader(new InputStreamReader(con.getInputStream()));
            StringBuilder sb = new StringBuilder();
            while ((response = br.readLine()) != null) {
                sb.append(response);

            }

            response = sb.toString();
            System.out.println(response);

        con.disconnect();
        } catch (MalformedURLException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    // Java Json

    ...
    import java.net.HttpURLConnection;
    import java.net.URL;


    public static void main( String[] args )
    {
        URL url;
        String response = "";
        try {

            url = new URL("https://lpr.recognition.ws/v2?accesscode=YOUR_ACCESS_CODE&format=JSON");

            final HttpURLConnection con = (HttpURLConnection) url.openConnection();

            final String imagePath = "YOUR_IMAGE_PATH";
            postImage(con, imagePath);

            BufferedReader br = new BufferedReader(new InputStreamReader(con.getInputStream()));
            StringBuilder sb = new StringBuilder();
            while ((response = br.readLine()) != null) {
                sb.append(response);

            }

            response = sb.toString();
            System.out.println(response);

        con.disconnect();
        } catch (MalformedURLException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    /////////////////////////////////////////////////////////////////
    /// function postImage(HttpURLConnection con, String filePath) //
    ////////////////////////////////////////////////////////////////

    public static void postImage(HttpURLConnection con, String filePath) {
        String charSet = "UTF-8";
        File binaryFile = new File(filePath);
        String boundary = "--";
        String CRLF = "\r\n";
        try {
            con.setDoInput(true);
            con.setDoOutput(true);
            con.setRequestMethod("POST");
            con.setRequestProperty("Content-Type", "multipart/form-data; boundary=" + boundary);

            OutputStream output = con.getOutputStream();
            PrintWriter pw = new PrintWriter(new OutputStreamWriter(output, charSet));
            pw.append("--" + boundary).append(CRLF);
            pw.append("Content-Disposition: form-data; name \"file\"; filename=\"" + binaryFile.getName() + "\"").append(CRLF);
            pw.append("Content-Type: image/gif").append(CRLF);
            pw.append(CRLF).flush();

            Files.copy(binaryFile.toPath(), output);
            output.flush();

            pw.append(CRLF).append("--" + boundary + "--").flush();

            pw.close();
            output.close();

        } catch (Exception e) {
            e.printStackTrace();
        }
    }

Swift(JavaScript, Python, C#, Java)



    // Swift XML

    import UIKit

    let url = URL(string: "https://lpr.recognition.ws/v2?accesscode=YOUR_ACCESS_CODE")
    let boundary = UUID().uuidString
    let session = URLSession.shared
    var urlRequest = URLRequest(url: url!)
    urlRequest.httpMethod = "POST"
    urlRequest.setValue("multipart/form-data; boundary=\(boundary)", forHTTPHeaderField: "Content-Type")
    let fileName = "YOUR_IMAGE_FILE_NAME"  // optional
    var img = UIImage(named: fileName)!
    var data = Data()
    data.append("\r\n--\(boundary)\r\n".data(using: .utf8)!)
    data.append("Content-Disposition: form-data; filename=\"\(fileName)\"\r\n".data(using: .utf8)!)
    data.append("Content-Type: image/png\r\n\r\n".data(using: .utf8)!)
    data.append(img.pngData()!)
    data.append("\r\n--\(boundary)--\r\n".data(using: .utf8)!)
    session.uploadTask(with: urlRequest, from: data, completionHandler: {responseData, response, error in
        if (error != nil) {
            print("error occurred")
        }
        if let responseString = String(data: responseData!, encoding: .utf8) {
            print("uploaded: \(responseString)")
        } else {
            print("error occurred")
        }
    }).resume()

    // Swift Json

    import UIKit

    let url = URL(string: "https://lpr.recognition.ws/v2?accesscode=YOUR_ACCESS_CODE&format=JSON")
    let boundary = UUID().uuidString
    let session = URLSession.shared
    var urlRequest = URLRequest(url: url!)
    urlRequest.httpMethod = "POST"
    urlRequest.setValue("multipart/form-data; boundary=\(boundary)", forHTTPHeaderField: "Content-Type")
    let fileName = "YOUR_IMAGE_FILE_NAME"  // optional
    var img = UIImage(named: fileName)!
    var data = Data()
    data.append("\r\n--\(boundary)\r\n".data(using: .utf8)!)
    data.append("Content-Disposition: form-data; filename=\"\(fileName)\"\r\n".data(using: .utf8)!)
    data.append("Content-Type: image/png\r\n\r\n".data(using: .utf8)!)
    data.append(img.pngData()!)
    data.append("\r\n--\(boundary)--\r\n".data(using: .utf8)!)
    session.uploadTask(with: urlRequest, from: data, completionHandler: {responseData, response, error in
        if (error != nil) {
            print("error occurred")
        }
        if let responseString = String(data: responseData!, encoding: .utf8) {
            print("uploaded: \(responseString)")
        } else {
            print("error occurred")
        }
    }).resume()