mp3tag does not show thumbnail

Many audio files have thumbnail images. Attached image shows mp3 file with thumbnail. However mp3tag does not detect this. Want to remove the thumbnail. Please help.

It looks as though you use the Windows Media Player.
This program uses two ways of storing images:
one in the album folder with the files folder.jpg and albumartsmall.jpg
(You have to set the Explorer to show hidden files to see these).
You would have to delete these two kinds of file in every folder.

And it has a Grafikcache in the folder
%appdata%\Local\Microsoft\Media Player\Grafikcache\LocalMLS
You can delete the whole folder LocalMLS.
This should get rid of any thumbnail that is not stored in the music files.