If information is "lost" through a lossy conversion, the images are different, and the code I posted will detect those differences.
Note well: The OP didn't ask to find images that "looked the same" or were "substantially similar", or any other form of fuzzy comparison.
He asked for:
I would like my script to compare two images and tell me if even one single pixel is slightly different in one of them.
Which is exactly what the code I posted--as opposed to your theory--does.
Hence, your "point" is pointless.
Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
"Science is about questioning the status quo. Questioning authority".
In the absence of evidence, opinion is indistinguishable from prejudice.