OpenALPR

// Initialize the library using United States style license plates.  
// You can use other countries/regions as well (for example: "eu", "au", or "kr")
alpr::Alpr openalpr("us", "/path/to/openalpr.conf");

// Optionally specify the top N possible plates to return (with confidences).  Default is 10
openalpr.setTopN(20);

// Optionally, provide the library with a region for pattern matching.  This improves accuracy by 
// comparing the plate text with the regional pattern.
openalpr.setDefaultRegion("md");

// Make sure the library loaded before continuing.  
// For example, it could fail if the config/runtime_data is not found
if (openalpr.isLoaded() == false)
{
    std::cerr << "Error loading OpenALPR" << std::endl;
    return 1;
}

// Recognize an image file.  You could alternatively provide the image bytes in-memory.
alpr::AlprResults results = openalpr.recognize("/path/to/image.jpg");

// Iterate through the results.  There may be multiple plates in an image, 
// and each plate return sthe top N candidates.
for (int i = 0; i < results.plates.size(); i++)
{
  alpr::AlprPlateResult plate = results.plates[i];
  std::cout << "plate" << i << ": " << plate.topNPlates.size() << " results" << std::endl;

    for (int k = 0; k < plate.topNPlates.size(); k++)
    {
      alpr::AlprPlate candidate = plate.topNPlates[k];
      std::cout << "    - " << candidate.characters << "\t confidence: " << candidate.overall_confidence;
      std::cout << "\t pattern_match: " << candidate.matches_template << std::endl;
    }
}