Simple script for xorring toghether all layers of a GIF image. This work with indexed image, working with multi-channel images could need some modifications.

xor-gif.py

#!/usr/bin/env python

import Image
import sys

def xorImage( infile ):
    try:
        im = Image.open( infile )
    except IOError:
        print "Cant load", infile
        sys.exit(1)
    (w,h) = im.size
    ss = [ [0]*w for x in range(h) ]
    try:
        while 1:
            m = im.load()
            for y in range(h):
                for x in range(w):
                    ss[y][x] ^= m[x,y]
            im.seek( im.tell() + 1 )
    except EOFError:
        im.seek(0)
        m=im.load()
        for y in range(h):
            for x in range(w):
                m[x,y]=ss[y][x]
        im.save(infile+'-xor.bmp')

if __name__ == "__main__":
    if len(sys.argv) < 2 :
        print "GIF image xorrer. Xor all the layer of the image."
        print "\tUsage %s <imagefile>" % sys.argv[0]
        exit(-1)
    xorImage(sys.argv[1])