title: Python OpenCV How to draw ractangle center of image and crop image inside rectangle?
body: <p>I use Python3 OpenCV3. I want to draw ractangle center of image and crop image inside rectangle.
  I try to run this code but rectangle not show at the center of image.</p>
  
  <pre><code>width, height, channels = img.shape
  cv2.rectangle(img,(0,0),(int(width/2), int(height/2)), (0,255,0) , 2)
  </code></pre>
  
  <p>How to draw ractangle center of image and crop image inside rectangle ?</p>