Hide messages in images and get them back.

hidemessage.py

# Hiding Messages in Images
#
# 
# Just do this to encode messages:
#
# python hidemessage.py -e <filewithmessage> <imagetohidein>
#
# 
# ...and do this to decode messages:
#
# python hidemessage.py -d <imagetodecode>
#
# 
# End messages with one ` to tell the decoder when to stop. PNGs recommended.
# 
# Python 2.7.5+, requires OpenCV.

import sys, getopt, cv2, base64, binascii

"""
Encode message in image
"""
def encode(img, msg):
    binmsg = "".join('{:08b}'.format(ord(c)) for c in msg)
    msgcounter = 0
    for x in range(0, img.shape[1]):
        for y in range(0, img.shape[0]):
            for c in range(0,3):
                iodd = img[y, x, c] % 2
                modd = binmsg[msgcounter]
                if iodd != int(modd):
                    if img[y,x,c] == 255:
                        img[y, x, c] -= 1
                    elif img[y,x,c] == 0:
                        img[y,x,c] += 1
                    else:
                        img[y,x,c] -= 1
                if msgcounter+1 < len(binmsg):
                    msgcounter += 1
                else:
                    return img
    return img

"""
Decode message from image
"""
def decode(img):
    characters = []
    for x in range(0, img.shape[1]):
        for y in range(0, img.shape[0]):
            for c in range(0,3):
                characters.append(str(img[y, x, c] % 2))

    binmsg = "".join(characters)
    msglist = []
    for c in range(0, len(binmsg), 8):
        char = chr(int(binmsg[c:c+8], 2))
        if char != "`":
            msglist.append(char)
        else:
            break

    return "".join(msglist)

def usage():
    print("""Usage: python message.py [ options... ] [image]
    -e/--encode [file] -- Encode message in given file
    -d/--decode -- Decode message""")

def main(argv):
    try:
        opts, args = getopt.getopt(argv, "he:d", ["help", "encode=", "decode"])
    except getopt.GetoptError:
        usage()
        sys.exit(2)

    img = cv2.imread(args[0])

    for opt, arg in opts:
        if opt in ("-h","--help"):
            usage()
            sys.exit()
        elif opt in ("-e", "--encode"):
            with open(arg, 'r') as thefile:
                message = thefile.read()
            codedimage = encode(img, message)
            cv2.imwrite("coded.png", codedimage)
        elif opt in ("-d", "--decode"):
            message = decode(img)
            print(message)

if __name__ == '__main__':
    main(sys.argv[1:])