mozaiq's encryption page allows people to hide secret messages inside images. Using this decryption page, you can reveal those messages.
Find the image that was has a message emedded in it. Upload it using the form at the right. If the image was encrypted with a password, be sure to enter it as well or you won't be able to uncover the message.
If you don't have an image with and embedded message, or you want to make your own, check out mozaiq's encryption page.