As a previous post mentioned, the metadata for Groove is in an ESENT database. One of the big questions is where does it get its artwork from?
Album Artwork
Groove will get its album artwork from one of two places: from the file metadata or from xbox catalog web services at http://musicimage.xboxlive.com (probably former Zune services). It does not use folder.jpg, nor does it use ZuneArt_{guid}.jpg. It will only access the web services if you have the Media Info option set to automatically retrieve missing metadata.
In order to get good album artwork, your metadata needs to be pristine and has to match what’s in the xbox metadata services. That’s unreliable at best. The best solution is to embed your artwork in your media files.
If you want to wipe out your library and rebuild from scratch, you can rename the randomly-(or not)-named folder in:
%userprofile%\AppData\Local\Packages\Microsoft.ZuneMusic_8wekyb3d8bbwe\LocalState\Database
Why wipe out the library? If you have a massive amount of artwork that originally was downloaded from the xbox services and now you have all that artwork in your media files, it’s faster to let Groove rescan your library than to update each album’s artwork.
As Groove is collecting the album art, it keeps a cache of the images in:
%userprofile%\AppData\Local\Packages\Microsoft.ZuneMusic_8wekyb3d8bbwe\LocalState\ImageStore
It doesn’t seem to matter if the image comes from the file or from the web services.
Artist Images
How, when and where does Groove get its artist info?
Although the ID3 specification does provide a way to embed an artist image, there isn’t currently a common utility that lets you do it. Doesn’t matter anyway since Groove doesn’t read the metadata fro artist images.
Like the album art cache, artists are stored in:
%userprofile%\AppData\Local\Packages\Microsoft.ZuneMusic_8wekyb3d8bbwe\LocalState\ImageCache\20
And the way Groove gets the artist images is by searching the music.xbox.com site based on your metadata. If there’s no match,m or if music.xbox.com doesn’t have that artist in the marketplace, that’s about where it ends. There doesn’t appear to be a way to override this yet.