My colleague remembers and old backup tool, packaged as a standard bootable ISO image. He thinks the file was about ~250 MB, containing a MD5SUM.txt, which included the MD5 Checksum of the entire ISO image.
I am no crypto/hash expert, but according to my understanding of checksum methods, he is wrong. He should have downloaded checksum separately, or else, the vendor should have had a hard time guessing the right MD5 such that adding it's hex form in a text file beside all other contents of the image makes the exact same checksum, right? I can't think of any shortcut to calculate such checksum.
(Unfortunately we don't have the ISO right now, so that I can win the bet and get a free beer.)