OpenCV

#include <opencv2/core/core.hpp>
#include <opencv2/highgui/highgui.hpp>
#include <opencv2/objdetect/objdetect.hpp>
#include <iostream>

using namespace std;
using namespace cv;

const String haarcascade_face = "haarcascade_frontalface_alt2.xml";
const String window_name_original = "OpenCV Demo Camera Face Detection - Original";
const String window_name = "OpenCV Demo Camera Face Detection";

int main(int, char**)
{

    Mat frame;

    VideoCapture capture;

    CascadeClassifier cascade;

    if(! cascade.load(haarcascade_face))
    {

        cout << "Could not open the Haar Cascade file!" << endl;

        return -1;

    }

    if(! capture.open(0))
    {

        cout << "Could not open or find the camera!" << endl;

        return -1;

    }

    namedWindow(window_name, CV_WINDOW_AUTOSIZE);

    namedWindow(window_name_original, CV_WINDOW_AUTOSIZE);

    for(;;)
    {

        capture >> frame;

        if(! frame.data) break;

        imshow(window_name_original, frame);

        vector<Rect> faces;

        cascade.detectMultiScale(
                    frame,
                    faces,
                    1.1,
                    3,
                    0,
                    Size(20, 20));

        vector<Rect>::const_iterator i;

        for(i = faces.begin(); i != faces.end(); i++)
        {

            rectangle(frame, Point(i->x, i->y), Point(i->x + i->width, i->y + i->height), CV_RGB(255, 0, 0), 2);

        }

        imshow(window_name, frame);

        char c = cvWaitKey(1);

        if(c == 27) break;

    }

    return 0;
}