sudo readom dev=/dev/sr0 f=~/image.iso
Replace /dev/sr0 for your optical device.
If the drive is mounted you can find it by typing
sudo mount
and looking for a line like
/dev/sr0 on /media/cdrom0 type iso9660 (ro,nosuid,nodev,utf8,user=foo)
In Debian make sure the device is not mounted or you will get the error:
Error trying to open /dev/sr0 exclusively (Device or resource busy)... retrying in 1 second.
Error trying to open /dev/sr0 exclusively (Device or resource busy)... retrying in 1 second.
Error trying to open /dev/sr0 exclusively (Device or resource busy)... retrying in 1 second.
Error trying to open /dev/sr0 exclusively (Device or resource busy)... retrying in 1 second.
Error trying to open /dev/sr0 exclusively (Device or resource busy)... giving up.