Backup before every change
Before scaling or compression replaces a file, the original is copied to a protected backup folder. If the backup cannot be created, the action is aborted — the plugin never changes anything it cannot revert.
Two ways to restore
Undo last action steps back one change at a time. Restore original jumps straight back to the very first version. Both are row actions in the image list; the bulk action restores originals.
Storage
Backups are kept indefinitely by default. Under Settings → Backup you can enable automatic cleanup after 30/60/90 days and get a warning when backups grow beyond your chosen limit.