import os
import math
import operator
from PIL import Image

original = r"C:\working\exiftool\example\for_checks\cover_original.jpg"
exif_fixed = r"C:\working\exiftool\example\for_checks\cover_exif.jpg"
hand_fixed = r"C:\working\exiftool\example\for_checks\cover_hand_fixed.jpg"
small_line = r"C:\working\exiftool\example\for_checks\small_line.jpg"
all_black = r"C:\working\exiftool\example\for_checks\all_black.jpg"
inverted = r"C:\working\exiftool\example\for_checks\inverted.jpg"

def find_rms(image1, image2):
    h1 = Image.open(image1).histogram()
    h2 = Image.open(image2).histogram()
    rms = math.sqrt(reduce(operator.add, map(lambda a,b: (a-b)**2, h1, h2))/len(h1))
    print "rms: {} - Source images: {} and {}".format(rms, os.path.basename(image1), os.path.basename(image2))


find_rms(original, original)
find_rms(original, exif_fixed)
find_rms(original, hand_fixed)
find_rms(original, small_line)
find_rms(original, all_black)
find_rms(original, inverted)