title: Recognizing black and white images with OpenCV
body: <p>I have this set of images :</p>
  <p><a href="https://i.stack.imgur.com/77eBv.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/77eBv.png" alt="enter image description here" /></a></p>
  <p>The leftmost one is the reference image.</p>
  <p>I want to have a value telling me how close is any of the other images to the leftmost one.
  I experimented with matchShapes(), by calling it for each contour and averaging the values, but I didn't get useful result (the rightmost one had a too high value, for example)</p>
  <p>I would also want the matching to work only in the correct orientation.</p>