title: Gtk-WARNING **: cannot open display: raspberry pi opencv
body: <ul>
  <li>Raspberry Pi3 ModelB</li>
  <li>OpenCV 3.0.0</li>
  <li>python 3.6.x</li>
  </ul>
  
  <p>Cannot show image via openCV. ex) imshow() 
  here is my source code.</p>
  
  <pre><code>def show_captured_image(path):
      img = cv2.imread(path, 1)
      resize_img = cv2.resize(img, (480, 320))
      xy_axis = cv2.flip(resize_img, -1)
      cv2.imshow("img", xy_axis)
      cv2.moveWindow("img", 0, 0)
      cv2.waitKey(0)
  </code></pre>
  
  <p><code>(img:2984): Gtk-WARNING **: cannot open display:</code>
  occurs in this line.</p>
  
  <p>please tell me the solution!</p>