Open a terminal screen (console).
Just to be on the safe side, verify if it is mounted or not with the mount command.
If CD is reported as mounted (maybe it was automatically by the OS), use the umount command.
Create the ISO image with the dd command.
- if=/dev/sr0 : Read from /dev/sr0 (raw format)
- of=/mnt/home/image.iso : write to a file named image.iso