Online Steganography
This website provides you with the functionlity to hide files within pictures. This process is also known as Steganography.
"Steganography is the art and science of writing hidden messages in such a way that no one apart from the intended recipient knows of the existence of the message;" Wikipedia
What you need
A png picture
A secret file. This can be a zip file.
A key. (A key is like a password. You will need it to extract the secret file).