title: Show two images overlapping each other in openCV
body: <p>In Matlab there is a possibility to show two images overlapping each other, which is quite useful to show how two images are aligned with respect to each other.</p>
  
  <p>For instance look to following code:</p>
  
  <pre><code>img1 = zeros(100,100);
  img1(20:50, 10:40) = 255;
  img2 = zeros(100, 100);
  img2(35:65, 35:65) = 255;
  imshowpair(img1, img2);
  </code></pre>
  
  <p>which creates following image:</p>
  
  <p><a href="https://i.stack.imgur.com/IzpEd.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/IzpEd.png" alt="enter image description here"></a></p>
  
  <p>Is there any built-in function or any way in openCV library to do so (in c++)? </p>