//load cascade classifier
String cascadeName = "haarcascade_profileface.xml";
cv::CascadeClassifier cascade(cascadeName);

/* already used this option to load the xml file
if( !cascade.load( cascadeName ) )
{
     std::cout << "ERROR: Could not load classifier cascade" << std::endl;
    return -1;
}*/

//image from pc
Mat img = imread("faces.jpg", 1);

//convert to gray the img
Mat gray, smallImg(img.rows, img.cols, CV_8UC1 );
cvtColor( img, gray, CV_BGR2GRAY );
resize( gray, smallImg, smallImg.size(), 0, 0, INTER_LINEAR );
equalizeHist( smallImg, smallImg );

std::vector<Rect> faces;
cascade.detectMultiScale( smallImg, faces,
    1.1, 2, 0
    //|CV_HAAR_FIND_BIGGEST_OBJECT
    //|CV_HAAR_DO_ROUGH_SEARCH
    |CV_HAAR_SCALE_IMAGE, Size(30, 30)
     );