To hide a file behind a image file which means that if any one opens that image he will see the image only but if you open in a special way then you can open the hidden file behind the image.
Passwords are Stored and Transmitted in an encrypted form called a Hash. When a User logs on to a system and enters a password, a hash is generated and compared to a stored hash. If the entered and the stored hashes match, the user is authenticated (This is called the Challenge/Response).