It is surprisingly easy to create .iso file in Linux. I have tested the method on Ubuntu Feisty and I am sure it works on other distro as well.

Open up terminal:

Assume that /dev/cdrom is the location of CD/DVD-ROM

sudo umount /dev/cdrom
readcd dev=/dev/cdrom f=file.iso

That’s it.

If you want to mount your .iso file,

sudo mkdir /media/iso
sudo modprobe loop
sudo mount -t iso9660 -o loop file.iso /media/iso/

Sources: How to create Image (ISO) files from CD/DVD [Ubuntu Guide]