I’m using musicbrainz picard to tag some files. I have enabled the “Save cover images as separate files” option. This generally works, but when a cover image is not found from a provider, but there is an embedded cover image present, it is not saved as a file. Is there a way to save it as a file when an image from a provider isn’t found?
I know this doesn’t solve the problem, but I have a band-aid fix in the meantime and is how I also recover embedded art that I overwrite mistakenly with less desirable art from the web.
Any artwork that Picard loads, both from the web and embedded, gets saved to your temp files (the root of /tmp on linux) as a ‘picard.ext’. Since I have local artwork as my first source, if there isn’t a web image available and I haven’t extracted the embedded by providing a copy for Picard then I end up losing the art altogether. If I copy the artwork from the /temp directory (drag & drop works as well I believe, but I normally use the terminal to do so in case there’s a lot in there to sort through. picard lists the filename at the top of the preview window for artwork in question.)
hope you understand what i’m trying to explain there lol. i haven’t used Windows in a few years so I’m not sure where exactly the temporary files are stored there, but somewhere buried in your User folder you will find them 
I’d also love to see this fixed up or find out a solution that’s far easier that I’m not aware of but wanted to share a way to at least work-around the situation without using additional software, etc.