With Ubuntu, you can create ISO disk Images directly from CD/DVD and folder files. Then create MD5 Checksum files.
Assumed that the CD/DVD device is located at /dev/cdrom/

Turn a CD/DVD into an .iso
$ sudo umount /dev/cdrom
$ dd if=/dev/cdrom of=file.iso bs=1024

Turn a folder into an .iso
$ mkisofs -r -o file.iso /location_of_folder/

Generate an MD5 checksum file
$ md5sum file.iso > file.iso.md5

Check MD5 checksum of file
$ md5sum -c file.iso.md5

Not only for Ubuntu, you can also use this command to create ISO images and MD5 checksum in any Linux Distro.