Compare two images.

image_diff.py

# http://effbot.org/zone/pil-comparing-images.htm
from PIL import Image
import sys
import math
import operator

if len(sys.argv) < 3:
    print "<image_path> <image_path>".format(sys.argv[0])
    sys.exit(1)

img1 = sys.argv[1]
img2 = sys.argv[2]

print img1
print img2

h1 = Image.open(img1).histogram()
h2 = Image.open(img2).histogram()

rms = math.sqrt(reduce(operator.add, map(lambda a,b: (a-b)**2, h1, h2))/len(h1))

print "Difference (0.0 means images are identical):\n{0}".format(rms)