imshow opens window to be grey and freezes

edit

I'm new to opencv and starting by reading in an image, and trying to display. from the command prompt:

cd to the project directory, then:

import cv2

# Load a color image in grayscale
img = cv2.imread('oyster.jpg',0)
cv2.imshow('img', image)
cv2.waitKey(0)

it opens a windows10 window which is just grey and freezes.

Any pointers would be appreciated.