Square thumbnail with Python Image Library

Every once in a while someone will walk up to me and ask, "how do you make a square thumbmail using PIL (Python Image Library)"? To this I say:

import Image

THUMB_SIZE = 80, 80
img = Image.open("someimge.jpg")
width, height = img.size

if width > height:
   delta = width - height
   left = int(delta/2)
   upper = 0
   right = height + left
   lower = height
else:
   delta = height - width
   left = 0
   upper = int(delta/2)
   right = width
   lower = width + upper

img = img.crop((left, upper, right, lower))
img.thumbnail(THUMB_SIZE, Image.ANTIALIAS)
img.save("someimge-thumb.jpg")

They usually walk away satisfied...