Steganography is the art and science of concealing messages in other messages in such a way that no one, apart from the sender and intended recipient, suspects the existence of the message. It’s a form of security through obscurity. Steganography is often used with cryptography. Plainly visible encrypted messages, no matter how unbreakable they are, arouse interest. This weakness is avoided with steganography.
In most cases, no-one would even know there was a hidden message, so such means are not usually subjected to attempts to crack them.
See https://www.linuxlinks.com/best-free-open-source-steganography-tools