If you right click a cover in Book Details panel it copies the image bit map (not the file) into the clipboard, from there you need to paste it into an an image editor, and save it in the required image format - BMP, PNG, GIF, JPG etc.
IMO the safest way to
copy files from a book folder in Windows is :
- First put a regular shortcut to your Desktop into your Send To folder.
- Open book folder with 'O', and use right click Send To->Desktop.
- That will copy the file, unlike buttonless drag drop which will move it if its on the same drive (that's the safety aspect)
- From the desktop you can do want you want with the copied file.
BR