Imaging a hard drive is basically creating an exact mirror copy of the hard drive. The copy is bootable and can be blasted onto the same or new hard drive fairly quickly. Of course, it can get out of date since the image is "frozen" in time, so making an image every month is a good idea. However, it is also smart to make a file-by-file backup procedure for extra peace of mind. It is recommended to use both backup methods in order to conserve important media and files.