OpenCV: resize the image, ROI

int image_resize(IplImage *img,float factor)
{
IplImage *tmp;

tmp = vCreateimage(cvSize(img->width*factor,img->height*factor),8,3);

cvResize(img,tmp,CV_INTER_NN);
cvReleaseImage(&img);

cvCopyImage(tmp,img);
cvReleaseImage(&tmp);

return 0;
}
//ROI
IplImage* src = cvLoadImage("image.bmp", 3);
CvRect rect = cvRect(240, 360, 160, 120);
cvSetImageROI( src, rect ); // Sets the region of interest
cvSaveImage("roi.bmp", src);

// rotate image
double xshift, yshift;
iplGetRotateShift(90.0,124.0, 10.0, &xshift, &yshift);
iplRotate(file_image, dstimg, 10.0, xshift, yshift,
IPL_INTER_LINEAR );
Here is another example to choose ROI:

#include "stdafx.h"

#include< stdio.h>
#include< stdlib.h>
#include< cv.h>
#include< highgui.h>

int main()
{
IplImage* sourceimg = cvLoadImage("lena.bmp", 3);
CvRect r=cvRect(0,0,512,512);
cvSetImageROI(sourceimg,r);

CvMat *sub=cvCreateMat(r.width,r.height,sourceimg->depth);

//get sub-image in variable sub
cvGetSubRect(sourceimg,sub,r);

//pass that sub variable to an IplImage (extract the sub image from sourceimg)
IplImage *res=cvGetImage(sub,sourceimg);

//to align correctly (vertical flip)
//res->origin=1;

cvNamedWindow("Image",1);
 cvShowImage("Image",res);
 cvWaitKey(0);

 return 1;
 
}