Hi, I am beginner in OpenCV, so i download it and just for an example copied from the internet Background detection code, and i have only one error

edit

#include <opencv2/opencv.hpp>
#include <iostream>
#include <vector>


int main(int argc, char *argv[])

{

    cv::Mat frame;
    cv::Mat back;
    cv::Mat fore;
    cv::VideoCapture cap(0);
    cv::BackgroundSubtractorMOG2 bg;
    bg.set("nmixtures" , 3);
    bg.set("bShadowDetection", false);

    std::vector<std::vector<cv::Point> > contours;

    cv::namedWindow("Frame");
    cv::namedWindow("Background");

    for (;;)
    {
        cap >> frame;
        bg.operator ()(frame, fore);
        bg.getBackgroundImage(back);
        cv::erode(fore, fore, cv::Mat());
        cv::dilate(fore, fore, cv::Mat());
        cv::findContours(fore, contours, CV_RETR_EXTERNAL, CV_CHAIN_APPROX_NONE);
        cv::drawContours(frame, contours, -1, cv::Scalar(0, 0, 255), 2);
        cv::imshow("Frame", frame);
        cv::imshow("Background", back);
        if (cv::waitKey(30) >= 0) break;
    }
    return 0;
}


error : error C3861: normHamming: identifier not found  c:\program files\opencv\build\include\opencv2\features2d\features2d.hpp