Here is how to create an ISO image (file .iso) on your hard disk. Useful when needed to make multiple copy of a CD. The following example starts create it directly from CD but since in Linux everything is a file… 
mkisofs -D -o ~/my-cool-cd.iso /cdrom
the -D option allow the deep ISO9660 directory nesting.
You can easily use this command even from windows by installing the cygwin with the mkisofs package.
UPDATE
The command above it’s a bit strict. In order to create a more “relaxed” cd-rom you could use the following command
mkisofs -l -D -N -relaxed-filenames -V “Volume Label” -o ~/my-cool-cd.iso /cdrom
Here the options:
- -l: Allow full 31-character filenames. Normally the ISO9660
file-name will be in an 8.3 format which is compatible with MS-DOS,
even though the ISO9660 standard allows filenames of up to 31
characters. If you use this option, the disc may be difficult to
use on a MS-DOS system, but will work on most other systems. Use
with caution. - -D: Do not use deep directory relocation, and instead just pack them in
the way we see them. If ISO9660:1999 has not been selected, this
violates the ISO9660 standard, but it happens to work on many
systems. Use with cau- tion. - -N: Omit version numbers from ISO9660 filenames. This violates the
ISO9660 standard, but no one really uses the version numbers anyway.
Use with caution. - -relaxed-filenames: Allows ISO9660 filenames to include all 7-bit
ASCII characters except lowercase letters. This violates the ISO9660
standard, but it happens to work on many systems. Use with
caution.
