Solved: Windows Explorer shows generic thumbnails instead of embedded album art for music (mp3) files

I have a large number of mp3 files, all of them with embedded album art, but when viewing them via  Windows Explorer, I see generic music file icons instead of album art thumbnails.

Generic music icons.  Ugh.

I spent a good couple of hours troubleshooting this problem, so I would like to document the solution for anyone who happens to go through the same pain.

--- Rant Begin ---

The interwebz abound with questions posted from people who are having the same problem, but none of the solutions offered seemed to work for me. I have seen suggestions to download a registry file that will restore my mp3 file mapping, wipe my icon cache, go change various options in windows that control the displaying of thumbnails, etc. 

The most lame solutions are being offered from official Microsoft sources, which appear to have a policy of only giving answers that involve the User Interface of Windows, never going under the hood, never offering a life-saving hack, never suggesting the use of any tools that were not built by Microsoft.  I suppose they are being official like that.

And Microsoft has not made things easy at all, because there exist 3 different settings in the Windows User Interface that control the displaying of thumbnails:

1. In "Folder Options", the "Always show icons, never thumbnails" setting, which must be off.

2. In "System Properties", under "Performance", the "Show thumbnails instead of icons" setting, which must be on.

3. In "Group Policy Editor", the "User Configuration / Administrative Templates / Windows Components / Windows Explorer / Turn off the display of thumbnails..." settings, which must be Disabled or Not configured.

But of course the problem is very rarely one of the above.  If a user accidentally has one of the above settings wrong, they are likely to notice the problem with image thumbnails long before they notice it with mp3 thumbnails.  So, when a user is searching for a solution to mp3 thumbnails, they usually do so because they have thumbnails working on images, and they are wondering why they are not working on mp3 files, which means that they have all of the above settings right.

--- Rant End ---

So, my problem simply turned out to be wrongly written mp3 tags, or to put it differently, mp3 tags written in such a way that Microsoft Windows Explorer could not read them, so it was showing generic icons instead.

Here is what I did to fix the problem:

1. I re-installed Windows Media Player.  I am not sure that this was necessary, (since it did not immediately fix the problem,) but it may be a pre-requisite.

2. I instructed my favorite mp3 tag editor to save mp3 file tags as follows:

    1. Write ID3v2.3 tags

    2. Do not use padding

    3. Write ID3v2 tags only.  (No ID3v1 tags.)

For completeness, here is a screenshot of all the mp3 tagging options that I used:

foobar2000 mp3 tagging options that work

Then, in order to cause tags to be rewritten, I selected all my files, I attached some random image as the "Disc" picture, (because I know I have no files with such a picture,) and voila, all of my album art appeared in Windows Explorer's "Icons" view.  Then, I removed the "Disc" picture from all files.