What you describe is called steganography. It's a very old technique, and the implications in the [lossy] digital realm are reasonably well-understood. Here's

What you describe is called steganography. It's a very old technique, and the implications in the [lossy] digital realm are reasonably well-understood. Here's some code that can be played with that relates to steganography in images: https://github.com/RoliSoft/Steganography/tree/master https://github.com/RoliSoft/Steganography/tree/master