How to restore bootcamp from a windows image backup

I see. If the disk image was made when BOOTCAMP was a larger size than it is now (for example, you backed up the 80GB partition but want to restore it to an 40GB partition), it can't be done. If BOOTCAMP is now larger than it used to be, there's a larger chance of it working (but it won't expand to fill the entire disk).

I'm not sure if it would work, but you could try Disk Image Recovery in Windows.

1. On the Windows desktop, navigate to Settings > Update & Security > Recovery > Advanced Startup
2. When the blue options screen shows up, click Troubleshoot > System Image Recovery and follow the prompts

If the system restore won't work, I've heard WinClone, a Windows partition backup/restore tool, works well with Boot Camp.

Resizing partitions is not supported. It's easy to corrupt your partitions this way. First, try removing it with Boot Camp Assistant in macOS.

Remove Windows from your Mac using Boot Camp - Apple Support

If you aren't able to, or don't get all of the partition space back after removing it, you'll likely have to back up macOS with Time Machine (if you want), then erase it and restore from the backup.

1. Back up your Mac with Time Machine - Apple Support
2. Use Disk Utility to erase an Intel-based Mac - Apple Support
3. Restore your Mac from a backup - Apple Support