Stego.py

import Image

class ImageSequence:
    def __init__(self, im):
        self.im = im
    def __getitem__(self, ix):
        try:
            if ix:
                self.im.seek(ix)
            return self.im
        except EOFError:
            raise IndexError # end of sequence

i = Image.open("stego.gif")
w, h = i.size
a = []
t = []
for j in range(w):
    t.append(0)
for j in range(h):
    a.append(t)
for f in ImageSequence(i):
    p = f.load()
    for j in range(h):
        for k in range(w):
            c = p[k, j]
            b = 1 if c < 32 else 0
            a[j][k] ^= b
n = Image.new("1", (w,h))
for j in range(h):
    for k in range(w):
        n.putpixel((k,j),a[j][k])
n.save("muxed.gif")