image shredding algorithm

shredding.py

from PIL import Image
from os import urandom

import random
import sys


def encode(in_file, out_file):
    # read pixel data from the image and put it in a flat list
    im = Image.open(in_file)
    data = list(im.getdata())

    # generate a random seed which will be the key and shuffle the data
    seed = urandom(20).encode('hex')
    random.seed(seed)
    random.shuffle(data)

    # create and save the new image
    out = Image.new(im.mode, im.size)
    out.putdata(data)
    out.save(out_file)
    return seed

def decode(seed, in_file, out_file):
    # read the pixel data from the image and put it in a flat list
    im = Image.open(in_file)
    data = list(im.getdata())

    # we need to perform the inverse operation we did in encode
    # with the seed we create a list with the original indexes
    order = range(len(data))
    random.seed(seed)
    random.shuffle(order)

    original_data = [0] * len(data)
    for index, original_index in enumerate(order):
        original_data[original_index] = data[index]

    # create and save the decoded image
    out = Image.new(im.mode, im.size)
    out.putdata(original_data)
    out.save(out_file)

def usage():
    print "usage:   shredding.py encode in_file outfile"
    print "         shredding.py decode seed in_file out_file"

if __name__ == '__main__':
    if '-h' in sys.argv or '--help' in sys.argv:
        usage()
        sys.exit(0)
    elif 'encode' in sys.argv:
        seed = encode(sys.argv[2], sys.argv[3])
        print "File successfully encoded"
        print "Seed:", seed
        sys.exit(0)
    elif 'decode' in sys.argv:
        decode(sys.argv[2], sys.argv[3], sys.argv[4])
        print "File successfully decoded"
        sys.exit(0)
    else:
        usage()
        sys.exit(0)