opencv haarcascade usage

    cv::CascadeClassifier face_cascade;
    face_cascade.load("C:/OpenCV-3.2.0/opencv/sources/data/haarcascades/haarcascade_frontalface_alt2.xml");
    std::vector<cv::Rect> faces;
    face_cascade.detectMultiScale(frame, faces, 1.1, 2, 0|CV_HAAR_SCALE_IMAGE, cv::Size(30, 30) );

    // Draw circles on the detected faces
    for( int i = 0; i < faces.size(); i++ ){
        cv::Point center( faces[i].x + faces[i].width*0.5, faces[i].y + faces[i].height*0.5 );
        cv::ellipse( frame, center, cv::Size( faces[i].width*0.5, faces[i].height*0.5), 0, 0, 360, cv::Scalar( 255, 0, 255 ), 4, 8, 0 );
    }