Try using isoinfo(1) to extract an ISO image identifier
-rwxr-xr-x 3952 42_grml
-rw-r--r-- 567 Makefile
-rw-r--r-- 161 TODO
drwxr-xr-x - debian
drwxr-xr-x - etc
drwxr-xr-x - man
-rwxr-xr-x 4350 update-grml-rescueboot