Question: Would the following scenario be practical under real-world usage?
Let's say that you were to render your initial stenographed image as a BMP. Then let's say that you compress both the original image and the stenographed image into an identically compressed JPG setting (i.e. 90% JPG compression), and then proceed to upload both to the Internet Archive (does not manipulate / reformat images in any manner whatsoever).
Would the above scenario even be practical? The basic idea here, is to obfuscate the stenographed image enough to make detection at least a bit more difficult.
Naturally, each oth the two images would be stored on separate and unique Archive pages.
Not remotely. Steganographed data is put into the lowest order bits of the image. JPEG compression is lossy. When you convert BMP->JPEG->BMP, the resulting image will not have the same low order bits as the inputs.