Hidden cover art

I have some CDs that don't appear to have any cover art in mp3tag, but music players such as WMP and Sonos see it OK. Seems to be in some old stuff that I cleaned with TuneUp a few years ago. Is there a way to find the hidden cover art and make it show up in mp3tag.

Thanks for a brilliant app to sort out my library but I wish there was a better user guide because I don't understand a lot of what it does.

Check the folders of the files and see if there are hidden files with the name folder. jpg and/or albumartsmall.jpg. You can import these files into the audio files with MP3tag.

The media players sometimes maintain a proprietory database that stores such images. There is hardly any way to retrieve them.
WMP also maintains a graficcache directory where it stores images. perhaps you can dig into that.
But I guess it would be much easier to use one of the web sources to download the images again.

Hmm. I expect you're right but not sure. There aren't any hidden files in the library for the CD in question. Yes, WMV may have it in its cache but how did Sonos find it over on my NAS - magic? I do wonder if TuneUp makes its own secret album art tag that I haven't found in mp3tag and which mp3tag doesn't normally look into? Is that possible, or have I misunderstood?

No, that is not possible. Either the image is embedded in the file at a place where everybody finds it or there is none.
So try the web sources.

Fair enough, although I'm still struggling to think where Sonos found the image on my NAS if it wasn't in the tags. As it happens this particular album art doesn't show up anywhere, which is why I was investigating.

Thank you.