I think the reason you are not getting a response is that the definition of each is too wide. But, briefly:
A system image is an exact copy of a drive/partition, in its existing state.. By default, a system image includes the drives required for Windows to run. It also includes Windows and your system settings, programs, and files. You can use a system image to restore the entire contents of your computer, with your installed programs, to its last succesful state. If your hard disk or computer ever stops working, due to a software or virus malfunction, you use the image to replace the entire contents. It's a complete restoration - all of your current programs, system settings, and files are replaced with the contents of the system...