My suggestion is to attach a second hard disk or USB stick to store the image. If you have two USB sockets all the better but you can manage with one by swapping sticks. Load a copy of Linux on the second USB stick, its free and easy to install on USB. Boot from the Linux stick and either use a GUI application or terminal window to make an exact copy of your Windows copy to the USB used for storage.
Doing it in a terminal window:
Type 'lsblk' (without the quotes, it will list block storage devices)
Look for the one that matches the USB you want to store the image on, it will be something like 'sdc' or 'sdd'.
Look for the one that has Windows on it, probably 'sda' or 'sdb', the size should make it obvious.
Copy by typing this: 'dd /dev/<the windows drive> /dev/<the destination drive> status=progress'
That will give you a byte by byte copy of the original disk to the attached drive. Swapping the device names will reverse the process and overwrite the original with the copy.
I believe the installed copy of Windows will contain registration data specific to that machine, I don't think it can be copied to a different machine, at least without an intimate knowledge of editing the registry files. One of the reasons I gave up on Microsoft products a long time ago!