Manual ROI selection using mouse

#include <stdlib.h>
#include <stdio.h>
#include <math.h>
#include <string.h>
#include<opencv2\opencv.hpp>
#include <opencv2\highgui\highgui.hpp>

IplImage* frame, * img1;
CvPoint point;
int drag = 0;
CvCapture *capture = 0;
int key = 0;

void mouseHandler(int event, int x, int y, int flags, void* param)
{
/* user press left button */
if (event == CV_EVENT_LBUTTONDOWN && !drag)
{
point = cvPoint(x, y);
drag = 1;
}
/* user drag the mouse */
if (event == CV_EVENT_MOUSEMOVE && drag)
{
img1 = cvCloneImage(frame);
cvRectangle(
img1,
point,
cvPoint(x, y),
CV_RGB(255, 0, 0),
1, 8, 0
);
cvCopy(img1,frame, NULL);
cvShowImage("result", img1);
}
/* user release left button */
if (event == CV_EVENT_LBUTTONUP && drag)
{
img1 = cvCloneImage(frame);

cvSetImageROI(
img1,
cvRect(
point.x,
point.y,
x - point.x,
y - point.y
)
);

cvNot(img1, img1); // or do whatever with the ROI
cvResetImageROI(img1);
cvCopy(img1,frame, NULL);
cvShowImage("result", img1);
drag = 0;
}

/* user click right button: reset all */
if (event == CV_EVENT_RBUTTONUP)
{
cvShowImage("result", frame);
drag = 0;
}
}

int main(int argc, char *argv[])
{
capture = cvCaptureFromCAM( 0 );
/* always check */
if ( !capture ) {
printf("Cannot open initialize webcam!\n" );
exit(0);
}

/* create a window for the video */
cvNamedWindow( "result", CV_WINDOW_AUTOSIZE );
cvSetMouseCallback("result", mouseHandler, NULL);

while( key != 'q' ) {
frame = cvQueryFrame( capture );
cvShowImage("result", frame);
key = cvWaitKey( 1 );
}
cvDestroyWindow("result");
cvReleaseImage(&frame);
cvReleaseImage(&img1);
return 0;
}