title: Python OpenCV Error: Current thread is not the object's thread
body: <p>I'm having an error running simple code using cv2 module.</p>
  
  <p>It's just:</p>
  
  <pre><code>import cv2
  
  img = cv2.imread('sudoku.png',0)
  
  cv2.imshow('image',img)
  </code></pre>
  
  <p>And it fails with the following error:</p>
  
  <pre><code>QObject::moveToThread: Current thread (0x1b74720) is not the object's thread (0x1e57d70).
  Cannot move to target thread (0x1b74720)
  </code></pre>
  
  <p>I googled this error and tried a lot of things but it doesn't help. I tried installing without pip, I tried using step-by-step installation (from official OpenCV) but nothing helps.</p>
  
  <p>When I run:</p>
  
  <pre><code>cv2.__version__
  </code></pre>
  
  <p>It returns 3.4.3</p>