To create an exact image of a cd or dvd, you are able to use the dd command. If your disk is mounted at /mnt/disk, you can use this command to make an image file named disk.iso.
dd if=/mnt/disk of=/home/disk.iso
In that command, dd is the program that is used, if is the input file, and of is the output file. The result of that will be an exact copy of the disk in /home named disk.iso.