I need the boot.img file, so that to make a bootable disk. In these case, at least I saw the prompt Boot: and "Welcome" messages.
You don't need the boot.img file to make the CD.... it's in the ISO

Questions: Do we need to make the disk bootable? Just the ISO file good enough, no other files needed?
Yes, just the ISO burnt straight to CD. You end up with a bootable CD because the ISO is an "image" of a working bootable CD in the first place.

Keep trying