title: Copy an cv::Mat inside a ROI of another one
body: <p>I need to copy a <code>cv::Mat</code> image (source) to an ROI of another (Destination) <code>cv::Mat</code> image.</p>
  
  <p>I found <a href="https://stackoverflow.com/questions/7041181/equivalent-to-cvsetimageroi-in-the-opencv-c-interface">this reference</a>, but it seems that it does not work for my case.
  Do you have any pointers how could I do this using the OpenCV C++ interface?</p>