Herodotus wrote the Histories, which is widely consider the first work of written history, where he covered, among other things, the wars between the Greeks and the Persians - long before Alexander the Great would go on to finally end that conflict (although some might claim that Iran shooting missles into Israel is proof that they are not yet over). Herodotus also mentioned shaving the head of one of his messangers and marking a message (maybe with a tattoo), waiting for the hair to grow back, and sending the messanger to deliver the message. Representing information within a different message or object to avoid discovery - well that's known as Steganography.
Steganography means stetanos, or Greek for "concealed" and "graphia," Greek for writing. Some might argue that the Phoenicians gave some of the Greeks the idea, around the same time they provided many of the letters and phonitic pictographs that two of those letters, Alpha and Bet would combine to be, alphabet (not the company). Or maybe he got the idea from the Egyptians when he visited there. Back to the point... Today, steganagrophy is typically used to conceal a file within a file - or to let's say drop a pdf into a picture of, um, head tattoos for posteries sake. Or dragons.
Search for the word "Steganography" on the App Store and there are a few apps that automate this. Search on Github and find a veritable cornucopia of goodness. Such is the love of cryptography-adjacent projects for budding computer scientists. I'm going to use an example from the App Store for ease of use. The below shows a very not-flashy tool called TheHider. Simply open, select an image using the Original Picture field, and then a file to hide in the image using the Message File field, and click Perform to embed the file into the image itself.
Now, consider the below file:
The file type is supported, but the size is over 34 megs. It would take a really large image file to hide this in there. That's because you need space to hide things. You can't really encrypt something without increasing the size. One of the bigger challenges of our day. Use the Reveal tab to get your original file back. This is a simple app - there's no key. It's also possible to encrypt and then hide, but take note - hiding is not encrypting, just like security through obscurity is not... er... security. Happy Friday!