Getting Album Art from Tag Sources

I've been tagging all the mp3s I make from my vinyl, putting them in artist and album folders and then using Tag Sources Discogs to write tags and cover art to the files. Until yesterday, when I then opened Windows Media Player 12, the cover art showed in the library. (a folder.jpg also appeared in each album folder).

Today after I did the same thing with a load of albums, WMP doesn't show the art in the library pane, but does show it in Now Playing view. There is no folder.jpg created.

Presumably either Mp3tag or WMP was creating the folder.jpg automatically from the tags in the files and now isn't Why?

I know I can fix this manually album by album (eg "Extract Cover"), but it was working beautifully in bulk up to now. Any ideas?

I would check for files without cover first with a filter
%_covers% MISSING
And then there is an action "Export cover to file" where you can set as filename "folder" - this would add a file folder.* to each folder. If there is already a file called folder.jpg then you get the new file as folder(1).jpg - which you could easily delete with a command shell command:
del /s folder(?).jpg

In addition, I would like to draw your attention to the "Utils" button in the tag sources results dialogue. This button has a little menu where you can set, where the covers should be saved. The filename is defined in File>Options>Tag-Sources.

Thank you!
Under "Utils" I have now set BOTH "save image to file" and "save image to disc" and that does what I need. Happily, it seems to remember that setting for future operations.
It must have been set on both before - maybe I clicked and changed it without realising!

Now I need to fix the previous albums.. You say check for files without cover with a filter
%covers% MISSING How and where do I apply that filter?

At the bottom of the main window there is the filter input box.
If you are not sure, repeat pressing F3 until you see it.
There you type in the string that I suggested:
%_covers% MISSING

Thanks - a bit confused as when I do that and open my whole "music" folder it doesn't seem to filter the result. If I click the right-arrow on the right of the filter box, it brings up a list of fields.

You can see at the bottom in the status bar how many files are loaded and how many are actually displayed.
And: the missing property is addressed with %_covers% and not %covers%.

Actually I had the right filter (I copied and pasted from your message) but I think that would be checking for missing cover tags, wouldn't it? And I want to find album folders that don't have the folder.jpg file. Don't worry, it won't take long to do that manually and then export the cover tag to a separate file.

If the filter shows all your files (and the filter is correct) then that means that none of your files has an embedded cover.

So if that is the case, then I would suggest that you import the covers with an action of the type "Import cover from file" and the format string

Then apply the filter again - and all the files that now show do not have an embedded cover and also no folder.jpg file in the folder.

Sorry - I updated that reply and found it did work,
How do you clear the filter? I've tried clearing the filter box and even restarting mp3tag, . But it's still only showing files with no embedded cover. What's the trick?
Update - now it has cleared!!
Thanks for your help - take a break!