Aaarrrrrrggghhhh! Spent all day trying to get my head around the differences between the two versions of the Python wrappers for OpenCV. Basically, the old version is contained within the new wrapper. So for the new version:
import cv2 as cv
but for the old version – that works with all the tutorials online! – use:
import cv2.cv as cv
Grrrr – can’t believe it took me that long to work it out.