decode.py

from PIL import Image
import sys

def decode_image(img):
    """
    check the red portion of an image (r, g, b) tuple for
    hidden message characters (ASCII values)
    """
    width, height = img.size
    msg = ""
    index = 0
    for row in range(height):
        for col in range(width):
            try:
                r, g, b = img.getpixel((col, row))
            except ValueError:
                # need to add transparency a for some .png files
                r, g, b, a = img.getpixel((col, row))
            # first pixel r value is length of message
            if row == 0 and col == 0:
                length = r
            elif index <= length:
                msg += chr(r)
            index += 1
    return msg

image = Image.open(sys.argv[1])
decoded_text = decode_image(image)

print("your hidden message is:\n{}".format(decoded_text))