title: error: (-2:Unspecified error) The function is not implemented. Rebuild the library with Windows, GTK+ 2.x or Cocoa support
body: <p>I was working on a sign language detection project on jupyter notebook. While running the code for live detection I encountered an error as shown below:</p>
  <blockquote>
  <p>OpenCV(4.5.1) C:\Users\appveyor\AppData\Local\Temp\1\pip-req-build-1drr4hl0\opencv\modules\highgui\src\window.cpp:651: error: (-2:Unspecified error) The function is not implemented. Rebuild the library with Windows, GTK+ 2.x or Cocoa support. If you are on Ubuntu or Debian, install libgtk2.0-dev and pkg-config, then re-run cmake or configure script in function 'cvShowImage'</p>
  </blockquote>
  <p>The code that caused this error is:</p>
  <pre class="lang-py prettyprint-override"><code>while True: 
      ret, frame = cap.read()
      image_np = np.array(frame)
      
      input_tensor = tf.convert_to_tensor(np.expand_dims(image_np, 0), dtype=tf.float32)
      detections = detect_fn(input_tensor)
      
      num_detections = int(detections.pop('num_detections'))
      detections = {key: value[0, :num_detections].numpy()
                    for key, value in detections.items()}
      detections['num_detections'] = num_detections
  
      # detection_classes should be ints.
      detections['detection_classes'] = detections['detection_classes'].astype(np.int64)
  
      label_id_offset = 1
      image_np_with_detections = image_np.copy()
  
      viz_utils.visualize_boxes_and_labels_on_image_array(
                  image_np_with_detections,
                  detections['detection_boxes'],
                  detections['detection_classes']+label_id_offset,
                  detections['detection_scores'],
                  category_index,
                  use_normalized_coordinates=True,
                  max_boxes_to_draw=5,
                  min_score_thresh=.5,
                  agnostic_mode=False)
  
      cv2.imshow('object detection',  cv2.resize(image_np_with_detections, (800, 600)))
      
      if cv2.waitKey(1) &amp; 0xFF == ord('q'):
          cap.release()
          break
  </code></pre>
  <p>NB: I installed OpenCV using using pip install.</p>