How to clone a hard drive to an image that I can open later?

Use dd (replace sda1 with the partition you want to save):

sudo dd if=/dev/sda1 of=/home/user/backup.img

This will make a mountable image of a partition. Just be aware that this could take a while, and the image will have the size of the partition, not the files on it. In your case this would be 80GB. If you compress the image it should be about the size of the used space of your hdd.

Refer to DriveImaging: Creating Disc Images Using dd for a more comprehensive explanation.

Remastersys is a program that can create backups of your entire hard drive and then save it to a LiveCD, for example. You can also use it to create a custom Ubuntu distribution. It has a CLI and a GUI, so take your pick. In the GUI, choose the first option, Backup.

To install it,open Software center Then Edit -> Software Sources -> Other software (Tab) and click add and paste

deb http://www.geekconnection.org/remastersys/repository karmic/

Now close the software sources window and wait for repos to be refreshed and install remastersys.

My preferred method is to use a CloneZilla live CD. Download the .iso, burn it to disk with Brasero, put it into the machine you want to image, reboot, attach the destination drive, and follow the prompts. Be cautious when using dd, it's a very low level tool and mistakes can destroy data easily. If you want to make a byte-for-byte copy of an image, select CloneZilla's partition-to-partition option.