OpenCV HOG is not detecting people

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Hi,

Please have a look at the below code

#include "opencv2/imgproc/imgproc.hpp"
#include "opencv2/objdetect/objdetect.hpp"
#include "opencv2/highgui/highgui.hpp"

#include <stdio.h>
#include <string.h>
#include <ctype.h>

using namespace cv;
using namespace std;

void help()
{
    printf(
        "\nDemonstrate the use of the HoG descriptor using\n"
        "  HOGDescriptor::hog.setSVMDetector(HOGDescriptor::getDefaultPeopleDetector());\n"
        "Usage:\n"
        "./peopledetect (<image_filename> | <image_list>.txt)\n\n");
}

int main()
{
    Mat img;
    char _filename[1024];


    img = imread("C:/Users/yohan/Desktop/dogwalker.jpg");



    HOGDescriptor hog;
    hog.setSVMDetector(HOGDescriptor::getDefaultPeopleDetector());
    namedWindow("people detector", 1);

    for(;;)
    {
        vector<Rect> found, found_filtered;
        double t = (double)getTickCount();
        // run the detector with default parameters. to get a higher hit-rate
        // (and more false alarms, respectively), decrease the hitThreshold and
        // groupThreshold (set groupThreshold to 0 to turn off the grouping completely).
        hog.detectMultiScale(img, found, 0, Size(8,8), Size(32,32), 1.05, 2);
        t = (double)getTickCount() - t;
        printf("tdetection time = %gms\n", t*1000./cv::getTickFrequency());
        size_t i, j;
        for( i = 0; i < found.size(); i++ )
        {
            Rect r = found[i];
            for( j = 0; j < found.size(); j++ )
                if( j != i && (r & found[j]) == r)
                    break;
            if( j == found.size() )
                found_filtered.push_back(r);
        }
        for( i = 0; i < found_filtered.size(); i++ )
        {
            Rect r = found_filtered[i];
            // the HOG detector returns slightly larger rectangles than the real objects.
            // so we slightly shrink the rectangles to get a nicer output.
            r.x += cvRound(r.width*0.1);
            r.width = cvRound(r.width*0.8);
            r.y += cvRound(r.height*0.07);
            r.height = cvRound(r.height*0.8);
            rectangle(img, r.tl(), r.br(), cv::Scalar(0,255,0), 3);
        }
        imshow("people detector", img);
        int c = waitKey(0) & 255;
            break;
    }
    return 0;
}

This is the OpenCV code for detecting humans. But I noticed that this do not detect people in most cases, for an example, please have a look at the below image.

If you run the above code on this, this will not detect the person. What is wrong here? Please help.