A) Scanning Artwork automatically only works with Artwork in the Album folder with no files from other Albums in them. There is no way around this.
B) When moving files, MediaMonkey will offer to move accompanying files like Artwork when all media files are removed from the folder.
C) If you embed Art you don't run into any of these issues. When using external Art you'll need to follow some basic rules to get the best experience.

There is no such thing as 'Composition' so I use Album for it. One can have multiple composition on one CD and I would find it a bit clumsy to create subdirectories for roughly 10.000 albums, given the fact that MM can tag as I want. Its just not able to do it when a path changes or files are removed and added back again. I really like MM and would like to keep it that way. Please have a look at it; trust me, it's a bug, and a nasty one for me and probably other users.

When using external Artwork it is best to use Album folders and not store files from multiple Albums in the same folder.

Found the bug.
Artwork is not found or files loose attached artwork_links if Auto-organize has <Album> in the destination line as in ".\<Track#:2> - <Artist> - <Album> - <Title>" and different album names occur in the same file list and albums are added to the library after being auto-tagged this way.
Eg.:
01 - Frédéric Chopin - Piano Concerto No. 1 in E minor, Op. 11, CT. 47 - Allegro maestoso.flac
02 - Frédéric Chopin - Piano Concerto No. 1 in E minor, Op. 11, CT. 47 - Romance. Larghetto.flac
03 - Frédéric Chopin - Piano Concerto No. 1 in E minor, Op. 11, CT. 47 - Rondo. Vivace.flac
04 - Frédéric Chopin - Waltz for piano No. 3 in A minor, Op. 34-2, CT. 209 - Grande Valse brillante.flac
05 - Frédéric Chopin - Variations on 'La ci darem' from Mozart's Don Giovanni.. - Variations.flac
We see 'Piano Concerto..', 'Waltz for piano..' and 'Variations..' as three different albums, same CD.
It has now become impossible for MM to auto-tag the artwork, moreover, existing artwork is lost if album is removed from library and added thereafter. I have tried this on 3 different machines, one Vista and two Win7. They all behave the same in a very consistent way. MM 4.0.7.1511
As said before, I don't want to end up with manually added thm files.
Thanks for looking.

Log sent

Hugorx wrote:Did not import 2 files (did not match import criteria)
Failed to import 0 files

The first one indicates any files that weren't imported due to user settings. The last one indicates how many files MediaMonkey should have imported, but failed to do (generally due to file corruptions).

You can submit a debug log (step 4b) for the failed Artwork scan. I recommend that you remove the folder from the Library, then scan it back in while capturing the debug log. Then send the debug log to support: http://www.mediamonkey.com/forum/viewtopic.php?f=1&t=69

I just had another case where MM persistently fails to import the artwork.
The Scan results report says:
Library now has 58636 files
Search and update took 0:00
Imported 0 new files
Updated 0 files
Did not import 2 files (did not match import criteria)
Failed to import 0 files

Last two sentences contradict but I can live with that.
The two files would be two very normal jpg's and I recall having seen them as artwork before, well in place. (In some instances, MM seems to loose artwork as well.)
Could it be that some characters in the file name prevent MM from importing artwork?
Here's the name and path of the first track, 232 characters should not be the problem, I have a lot with more:
G:\Muziek\Klassiek\Johann Sebastian Bach (1685 - 1750)\Bach - Kantate BWV 76, Motette BWV 225 (VHa)\001 - J. S. Bach - Cantata No. 76, 'Die Himmel erzählen die Ehre Gottes,' BWV 76 (BC A97) - Die Himmel erzählen die Ehre Gottes.flac

That's in Windows Explorer where you can set files to hidden. Hidden files are ignored by MediaMonkey.

Lowlander wrote:PS. Make sure that added Artwork isn't set to hidden.

Well, I searched high and lo but could not find how to hide artwork. Can it be done for individual files or is it global?

PS. Make sure that added Artwork isn't set to hidden.

Thanks anyway, if one day I find a reason and/or solution, I'll post it here.

I can't reproduce (note I'm on 4.1 beta). I added some files without Artwork, used Auto-Organize Files, added image file to folder, rescanned parent folder and image was shown in MM.

Lowlander wrote: Did you move the Artwork files to the new location? If so Add/Rescan Files should pick it up.

That is exactly the problem. Add/Rescan fails to pick up later moved artwork after music files have been processed with 'Auto-Organize Files'
Unfortunately, it is not consistent in doing so.
Please try this:
1) Create a folder with .flac tracks of an Album (don't know for other formats)
2) DON'T add images to the folder
3) Add folder to MM Library (if not already) making sure automatic scanning of Artwork is ENABLED
4) Process the music files with 'Auto-Organize Files'
5) Add images to the folder
6) Press Add/Rescan to make MM pick up the added artwork
7) Look how MM sometimes fails to pick it up and will never again pick it up, no matter what you try
8 ) Try all of the above without 4)
9) Look how MM picks up the artwork just fine

Lowlander wrote:PS. Setting format for multiple images to folder.jpg under Tools > Options > Tags & Playlists will prevent the thm file.
Also see: http://www.ventismedia.com/mantis/view.php?id=9951

It is my - and others from MM4 on, it seems - experience that this way of implementing the artwork procedures is not quite liked. MM3 was more straightforward IIRC.

Hugorx wrote:However, when I press auto-organize - to make changes to the file names - BEFORE the artwork is tagged because I forgot it, MM wil not tag it anymore and display the artwork in the art & detail section, not with add/rescan nor auto-organize.

Did you move the Artwork files to the new location? If so Add/Rescan Files should pick it up.

PS. Setting format for multiple images to folder.jpg under Tools > Options > Tags & Playlists will prevent the thm file.
Also see: http://www.ventismedia.com/mantis/view.php?id=9951

I must add that even 'Delete all content from Library and Computer' and add them back again does not solve the problem.
I tried this: Delete all content, maintain library with 'optimize database (complete), restart MM.
Artwork is not displayed anymore no matter what I try with add/rescan or auto-organize and 'scan directories for Artwork' checked.