title: Create a steganographically hidden image with Pillow
body: <p>I'm trying to learn how to create a set of images like this: <a href="https://github.com/rohieb/zeromutarts-ctf/blob/master/xoxo/xoxo.md" rel="nofollow">this</a>. The idea is that there are two seemingly random images, but when you XOR them, you find a secret message. I want to use Python Pillow, probably along with a simple image editor like paint.net. So my question consists of a few parts:</p>
  
  <ol>
  <li>How do I generate an image full of random black or white pixels in Pillow.</li>
  <li>How can I ensure certain areas of my images aren't actually random, but instead identical, ensuring an XOR compare will reveal them.</li>
  </ol>