title: OpenCV python cropping image
body: <p>I've created black image, than I drew a red rectangle into this image. Afterwards I cropped this image and drew a another rectangle into  the <strong>cropped</strong> image using the command. <code>cv2.rectangle(crop,(50,50),(150,150),(0,0,255),3)</code></p>
  
  <p>Why does this second rectangle appears in the original image when I show it at the end? I expected to see just the first rectangle.</p>
  
  <pre><code>import cv2
  import numpy as np
  
  #create image
  image = np.zeros((400,400,3), np.uint8)
  
  #draw rectangle into original image
  cv2.rectangle(image,(100,100),(300,300),(0,0,255),3)
  
  #crop image
  crop = image[100:300,100:300]
  
  #draw rectangle into cropped image
  cv2.rectangle(crop,(50,50),(150,150),(0,0,255),3)
  cv2.imshow('Result', image)
  cv2.waitKey()    
  
  cv2.destroyAllWindows()
  </code></pre>