For that you also need a recovery CD which can be burnt from the imaging program. This CD boots from the optical drive (because your system is inoperable or non-existent in case of a disk replacement). For that you need to change the boot sequence in the BIOS to allow booting from the optical drive in lieu of the operating system disk partition.
The following are the settings you need to do when using free Macrium for imaging. You can download free macrium from here.
For the instructions how to setup Macrium and how to operate it, download this Zip folder. It contains the guidance as a PDF document or a PowerPoint presentation.
I have also made a 30 minute video that describes the whole imaging cycle including the recovery. You can watch the video on this site.