I would not leave backup images on the PC's built-in drives in the first place and I would not leave external drives permanently connected nor set cloud storage to auto-sync.
Store images on an external drive that remains disconnected when not in use, store images in cloud storage that is not auto-syncing, use a USB flash drive to save your image and then disconnect, or whatever other means.
Handle your backup images and backup storage manually. It's a little bit more work, but far less prone to problems - like having to sort out which automatic backup(s) have adware or even malware on them. No ? It can't happen to you ? Think again...
Good grief... now everyone that reads this article thinks that have to run out and buy a premium Acronis license - when a $4 USB Flash drive and Macrium Free will work just fine.