Computer Science 15-112, Spring 2014
Class Notes:  Steganography (Image Manipulation and Encryption)

1. See the Wikipedia page on Steganography
   Goal:  To conceal a private image inside a public image, creating an encoded image that looks like the public image but secretly contains the private image.  Then, to send the encoded image to a recipient who can then decode the image and reconstruct the original private image.
    
2. Start with this private image (download it to privateImage.gif):
   
    
3. Also start with this image (download it to publicImage.gif):
   
   
    
4. Run this code:   steganographyEncoder.py
    
5. And it produces this encoded image (stored in encodedImage.gif):
   
    
6. Let's see the public and encoded images side-by-side:
    

   original public image	encoded image for transmission

    

7. Now, send the encodedImage.gif to your recipient
   You may include some innocuous and irrelevant text, like: "Hey, can you believe this guy pitched a cat?!?  Seriously, no Photoshop here.  Amazing!"
    
8. Your recipient saves encodedImage.gif and then runs this code:  steganographyDecoder.py
    
9. And it produces this decoded image (stored in decodedImage.gif):
   

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