Exactly - or encrypted payloads hiding inside standard image file formats. Basically steganography. If all you want to send is a small encrypted text message, it should be possible to hide that in a large image (encoding in the LSB or whatever) in just a small percentage of pixels so that it doesn't fail statistical tests and is indistinguishable from real noise.

In my home directory is a 4GB random file. I suggest you should do this too. Vary the filename to taste. Some suggestions: the name of any active drug market or cyber threat actor.