Graphically diff similar images

diff.py

#!/usr/bin/env python3

from PIL import Image

def diff(image_a, image_b):
  pixels_a = image_a.load()
  pixels_b = image_b.load()

  width_a, height_a = image_a.size
  width_b, height_b = image_b.size

  if width_a != width_b or height_a != height_b:
    print("unequal sizes")
    return None

  diff = image_b.copy()
  diff_pixels = diff.load()
  diffed = False

  for x in range(width_a):
    for y in range(height_a):
      pixel_a = pixels_a[x, y]
      pixel_b = pixels_b[x, y]

      if pixel_a != pixel_b:
        diffed = True
        diff_pixels[x, y] = (255, 0, 0)

  if diffed:
    return diff
  
  return None

if __name__ == "__main__":
  for i in range(1, 24):
    a = Image.open("a-%d.jpg" % i)
    b = Image.open("b-%d.jpg" % i)
    
    result = diff(a, b)
    
    if result:
      print("differences found on page", i)
      result.save("diff-%d.png" % i)