A user on Twitter asks
The way to go here is with an action "Export cover to file" and a custom format string that resembles the directory structure (see this post on how to create actions in Mp3tag).
The format string can be a combination of placeholders that take information of the current file and plain text.
So to export all cover art to a folder (e.g.,
D:\Covers\) with the library structure preserved, a working format string would replace the current library path (the working directory that's loaded in Mp3tag) with the cover folder path and use the rest of the file path to create the directory structure and the correct filename.
This would export the cover of each audio file. If you only want to export one file per folder, you can use
folder would be the image file name (the file extension is determined during export as it can vary depending on the cover mimetype).