Image difference with OpenCV

#include <stdio.h>
#include <stdlib.h>
#include <iostream>
#include <fstream>

#include "cv.h"
#include "highgui.h"

using namespace std;

char imagename1[100] = "red1.jpg";
char imagename2[100] = "red2.jpg";

void diffImage(IplImage* img1, IplImage* gimg1, IplImage* img2, IplImage* gimg2, IplImage* res) {
    // saving 1st channel
    cvSetImageCOI(img1, 3);
    cvCopy(img1, gimg1);
    cvSmooth(gimg1, gimg1, CV_BLUR, 5, 5);
    cvResetImageROI(img1);

    // saving 1st channel
    cvSetImageCOI(img2, 3);
    cvCopy(img2, gimg2);
    cvSmooth(gimg2, gimg2, CV_BLUR, 5, 5);
    cvResetImageROI(img2);

    // comparison
    cvAbsDiff(gimg1, gimg2, res);
    cvCmpS(res, 20, res, CV_CMP_GE);
}

void calculateMovementCoordinates(
        IplImage* diff_img,
        CvPoint& upperLeft,
        CvPoint& lowerRight) {

    upperLeft = cvPoint(-1,-1);
    lowerRight = cvPoint(-1,-1);
    //int minFound = 0;
    for(int row = 0; row < diff_img->height; ++row) {
        const uchar *ptr = (const uchar*)(diff_img->imageData + row * diff_img->widthStep);
        for(int col = 0; col < diff_img->width; ++col ) {
            if( *ptr++ ) {
                if( upperLeft.y == -1  ) {
                    upperLeft.y = row;
                } else {
                    lowerRight.y = row;
                }
                if( upperLeft.x == -1 || upperLeft.x > col ) {
                    upperLeft.x = col;
                } else if( lowerRight.x < col ) {
                    lowerRight.x = col;
                }
            }
        }
    }
    //cvMinMaxLoc(diff_img,&min,&max,&minloc,&maxloc);

}

int main(int argc, char** argv) {
    IplImage* old_img;
    IplImage* gimg1;
    IplImage* new_img = 0;
    IplImage* gimg2;
    IplImage* diff_img;
    IplImage* display_img;
    CvCapture* g_capture = NULL;
    CvPoint upperLeft, lowerRight;

    cvInitSystem(argc, argv);

    // photo
    //IplImage* tmpimg1 = cvLoadImage(imagename1);
    //IplImage* tmpimg2 = cvLoadImage(imagename2);
    //new_img = tmpimg1;

    char *libraries;
    char *modules;
    cvGetModuleInfo(0, (const char**) & libraries, (const char**) & modules);
    printf("libraries: %s\n, modules: %s\n", libraries, modules);


    // webcam
    g_capture = cvCreateFileCapture("panda.mp4");
    //g_capture = cvCreateCameraCapture(0);
    new_img = cvQueryFrame(g_capture);

    CvSize size = cvGetSize(new_img);
    old_img = cvCreateImage(size, IPL_DEPTH_8U, 3);
    gimg1 = cvCreateImage(size, IPL_DEPTH_8U, 1);
    gimg2 = cvCreateImage(size, IPL_DEPTH_8U, 1);
    diff_img = cvCreateImage(size, IPL_DEPTH_8U, 1);
    display_img = cvCreateImage(cvSize(2*size.width,size.height), IPL_DEPTH_8U, 3);

    IplImage *left_img = cvCreateImageHeader(size,display_img->depth,display_img->nChannels);
    left_img->origin = display_img->origin;
    left_img->widthStep = display_img->widthStep;
    left_img->imageData = display_img->imageData;

    IplImage *right_img = cvCreateImageHeader(size,display_img->depth,display_img->nChannels);
    right_img->origin = display_img->origin;
    right_img->widthStep = display_img->widthStep;
    right_img->imageData = display_img->imageData + right_img->width*right_img->nChannels;

    cvNamedWindow("Surveillance", CV_WINDOW_AUTOSIZE);
    int i = 0;
    while (1) {
        ++i;
        //new_img = i % 2 ?  tmpimg1 : tmpimg2;
        new_img = cvQueryFrame(g_capture);
        if (new_img) {
            diffImage(old_img, gimg1, new_img, gimg2, diff_img);
            cvCopy(new_img, old_img);
            cvSetImageCOI(left_img,1);
            cvCopy(diff_img,left_img);
            cvSetImageCOI(left_img,2);
            cvCopy(diff_img,left_img);
            cvSetImageCOI(left_img,3);
            cvCopy(diff_img,left_img);
            cvResetImageROI(left_img);
            calculateMovementCoordinates(diff_img, upperLeft,lowerRight);
            cvRectangle(new_img,upperLeft,lowerRight,cvScalar(0,0,255),6);
            cvCopy(new_img,right_img);
            cvShowImage("Surveillance", display_img);
        }

        char c = (char) cvWaitKey(10);
        if (c == 27) break;
    }
    cvReleaseImageHeader(&left_img);
    cvReleaseImageHeader(&right_img);
    cvReleaseImage(&display_img);
    cvReleaseImage(&old_img);
    cvReleaseImage(&gimg1);
    cvReleaseImage(&gimg2);
    cvReleaseImage(&diff_img);
    cvDestroyWindow("Surveillance");
    return (0);
}