for images the amount of hidden data is significantly less than the file size

1Mb jpeg with 8,388,608 pixels can hold about 349,525 pixels of secondary image

I know I said "about" and then specific pixel counts but that's what the calculation said.

The state of the art gives an embedding efficiency of 20 so I used that and 1Mb pulled out of thin air just to use as an example

https://link.springer.com/article/10.1007/s00500-023-09130-8