dd command to create an ISO image

Put CD into CDROM
Do not mount CD. Verify if cd is mounted or not with mount command:
    # mount
If cd was mouted automatically unmount it with umount command:
    # umount /dev/cdrom
OR
    # umount /mnt/cdrom

Create CD-ROM ISO image with dd command:
    # dd if=/dev/cdrom of=/tmp/cdimg1.iso

Where,
# if=/dev/cdrom: Read from /dev/cdrom (raw format)  of=/tmp/cdimg1.iso: write to FILE cdimg1.iso

i.e. create an ISO image