I believe the only sure way is to make the image before activation since Windows 7 can be fussy about holding activation even when reimaged to the same hardware, no matter what imaging utility is used.
You can try reinserting the Product Key at the "Change Product Key" link at Computer>Properties. If that link is missing, this can be done by opening an elevated Command Prompt to type slmgr -ipk
followed by a space and the Product Key. You can then reactivate at Computer>Properties or using slmgr -ato
Even worse is if it changes drive letter during reimaging and you start up to a black screen with non-Genuine and are locked out of the OS - requiring use of Paragon Rescue CD to boot and correct drive letter: Moving Win7 Partition to Another Drive
We get that at least once a month here.