The ISO images contain a directory .disk with some files. # cat .disk/info Debian GNU/Linux 9.2.1 "Stretch" - Official amd64 NETINST 20171013-13:07 Inside the d-i calling blkid /dev/sr0 outputs something like this: /dev/sr0: UUID="2017-10-13-13-09-57-00" LABEL="Debian 9.2 amd n" TYPE="iso9660" ..... I think the first is more d-i specific. -- regards Thomas