get stamp id3 tag editor http://www.nch.com.au/tageditor/index.html from this link now go to stamp id3 and open up the album you want to add thumbnail ,highlight all tracks in album and click on embeed then browse for album art then hit the stamp button and its that simple for your library to look good with all showing the album covers.
Thank you for sharing.
I use audio shell tag editor as it it supports most formats and I have everything in FLAC. It is a shell extension that allows you to edit the tags and ad covers for : MP3 (all ID3v2 tag versions), WMA, ASF, WMV, Apple iTunes AAC (M4A and M4P), MP4, OGG, FLAC (vorbis comment tags), MPC, MP+, monkey’s audio, WAV pack, optim frog (APE and APEv2 tags).
Made my life alot easier and works very well