This takes me back to when I was a young boy, and I used to get these James Bond magazines. They used a slightly different technique, but basically there was an

This takes me back to when I was a young boy, and I used to get these James Bond magazines. They used a slightly different technique, but basically there was an image that just looked like random noise like the images shown here, and you'd place a coloured plastic filter over it to reveal a hidden message. Very interesting stuff.