Many thanks Scotty, your responses are helpful.  But I need one clarification, as the link to the ghost protocol was too general.
 
My specific question is:
-          Having cloned my hard-drive using the EaseUS ghost software, in a subsequent, [differential] back-up process (monthly ish), how do I effect?  Choices appear to be:
o   File back-up
o   Smart back-up?  this gives the option of checking any of the following, which seems to make most sense, but not clear if this is differential back-up
§  Library                                  this is not checked
§  My documents                 this is checked
§  Favorites                             this is checked
§  Desktop                               this is checked
§  “Computer”                       this has a box that is filled in vs checked, and the sub folder shows OS (C)
 
I have reviewed the link you sent me and another hour trying to figure this out.  Your help appreciated
___________

Smart Backup is, in my opinion, the best option. It allows Ghost to check for added data and include that into previous backup images. That is the selection I would chose in your case. This is an “incremental backup”. In other words, it only adds changes or additions of files to the original full backup. A differential backup (not my preferred choice) copies all changed or additional files since the first day each time there is a backup.

Here’s Easeus knowledge base article on Smart Backups:
EaseUS Todo Backup - Smart Backup

For additional info and comparisons between different backup methods within Ghost check out this video and article as well:
Difference Among Full, Incremental and Differential Backup

In short, chose smart backup.

Disclaimer: I am an Apple Consultant and not a Windows specialist. For the best advice, you’ll want to seek the knowledge of a Microsoft certified consultant.