Simple steganography script using cv2

stego.py

import cv2

# Make a generator object for the message to be hidden
def char_generator(message):
	for c in message:
		yield ord(c)

# Convenience function for getting image
def get_image(image_location):
	img = cv2.imread(image_location)
	return img

# We'll use this as the pattern for picking pixels to write to
def gcd(x, y):
	while(y):
		x, y = y, x % y
		
	return x
	
def encode_image(image_location, msg):
	img = get_image(image_location)
	msg_gen = char_generator(msg)
	pattern = gcd(len(img), len(img[0]))
	for i in range(len(img)):
		for j in range(len(img[0])):
			if (i+1 * j+1) % pattern == 0:
				try:
					img[i-1][j-1][0] = next(msg_gen)
				except StopIteration:
					img[i-1][j-1][0] = 0
					return img

def decode_image(img_loc):
	img = get_image(img_loc)
	pattern = gcd(len(img), len(img[0]))
	message = ''
	for i in range(len(img)):
		for j in range(len(img[0])):
			if (i-1 * j-1) % pattern == 0:
				if img[i-1][j-1][0] != 0:
					message = message + chr(img[i-1][j-1][0])
				else:
					return message

Example usage in Python console:

>>> import stego
>>> secret_message = "Hello from inside the picture!"
>>> img_location = "test_img.jpg"
>>> img = stego.encode_image(img_location, secret_message)
>>> import cv2
>>> cv2.imwrite("output.jpg", img)
True
>>> encoded_pic_location = "output.jpg"
>>> stego.decode_image(encoded_pic_location)
'Hello from inside the picture!'
>>>