1. Insert the CD or DVD that you want to make an ISO image of.

2. Open a terminal window.

3. Execute the following command:

cat /dev/scd0 > /home/shamanstears/test.iso

Where /dev/scd0 is the device name for your drive (to find this, go to the Main Menu, click on System, mouseover Administration and select System Monitor. Click the File Systems tab. The device name will be listed in the Device column). Also make sure to change the path and iso filename to the desired path and filename.

The disc will begin to spin and the ISO image will start being constructed. Once it has completed, you have an ISO image of your CD. To verify that the image was properly created, mount the ISO file and check the contents.

This was taken from here.

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 

How to Mount and Unmount ISO Files

1. Open a terminal window.

2. You will need to create a new directory for your ISO image. Execute the following command in your terminal window:

sudo mkdir /media/iso

3. Now execute this command to mount the ISO image:

sudo mount -o loop /home/shamanstears/Documents/test.iso

Make sure to change the path in the above command to the path of the desired ISO file.

4. Close the terminal window.

5. Go to the Ubuntu Main Menu.

6. Click Places and select iso.

7. The file browser will open, displaying the contents of the ISO image.

To unmount the file, use this command in a terminal window:

sudo umount /media/iso/

This was taken from here.