Are you using the Windows 7 Key originally associated with that system? As I understand it, you have a desktop and a laptop. The laptop you upgraded to Windows 10 first. As per your original post, it worked fine there. Then I presume you installed Windows 10 to your desktop, and found it didn't work, so you reinstalled Windows 7... or you mention you wanted to reverse it so the laptop had Windows 7 and the desktop had Windows 10.
One thing to remember is you cannot use the Win7 key on a new install if that Win7 Key is the same key in use on an active Windows 10 install. That is, if you upgrade the laptop to Windows 10, you cannot use the Windows 7 key that was on that system for a Windows 7 install elsewhere.
I also don't see an response to your original question regarding System Image creation- you can create a disk image using something like Macrium Reflect. The main thing is that where you store the image should be larger than the drive you want to make an image of. It saves absolutely everything on that drive- if you make a system image of a Windows 7 install, upgrade to Windows 10, and then restore the disk image, it will be back to windows 7 exactly as it was before.
Why should i have to? I have a perfectly legitimate product key purchased with the computer but now Microsoft wont accept it because i have had to reinstall the Software it relates to. All because their precious Windows 10 messed up the machine!!
You are trying to jump back and forth a bit here. You upgraded your laptop to Windows 10, you want to upgrade your desktop to Windows 10 but you want to rollback the laptop to Windows 7. Presumably you did upgrade the desktop to Windows 10 so now you want to roll that back as well since it gave you problems afterwards. You would have to use the appropriate Win7 key for each of them when reinstalling. I would expect the license servers work to detect when you downgraded by going "OK, is this the same hardware as we found when they upgraded this key to Windows 10?" And if so, it reassociates the key.
No doubt if the Windows 7 installs were already on the system (eg they were sold with Win7) that could complicate things as well as that is a whole other can of worms.