text: #include <iostream>
  #include <opencv2/opencv.hpp>
  
  const std::string keys =
          "{help      |           | print this message    }"
          "{@image    |lena       | load image            }"
          "{lena      |lena.jpg   | lena image            }"
          ;
  
  int main(int argc, char *argv[])
  {
      cv::CommandLineParser parser( argc, argv, keys);
      parser.about("Load image and display");
      if (parser.has("help")){
          parser.printMessage();
          return 0;
      }
  
      cv::Mat srcImg;
      std::string file = parser.get<std::string>(0);
      if( file == "lena" ){
          file = parser.get<std::string>("lena");
      }
      srcImg = cv::imread(file, cv::IMREAD_COLOR );
      if( srcImg.empty() ){
          return -1;
      }
  
      cv::imshow("display windows", srcImg );
      cv::waitKey(0);
  
      return 0;
  }
  