Hi. An Image ISO claimed on official Debian
page to be an "
hybrid" ISO, with those properties
$ file -b debian-9.7.0-amd64-DVD-3.iso
ISO 9660 CD-ROM filesystem data 'Debian 9.7.0 amd64 3'
and which has been written to an external flash drive relying on that command
$ dd if=debian-9.7.0-amd64-DVD-3.iso of=/dev/sdc bs=4M oflag=direct && sync
could not even be launched at boot due to error message:
Reboot and select proper boot device or insert boot media in selected boot device and press a key.
while a Live ISO image debian-live-9.7.0-amd64-gnome.iso with those properties could
$ file -b debian-live-9.7.0-amd64-gnome.iso
DOS/MBR boot sector; partition 2 : ID=0xef, start-CHS (0x3ff,254,63), end-CHS (0x3ff,254,63), startsector 1416, 832 sectors