i Tunes, for example, does not automatically embed album art in your ID3 tags and the process for doing so depends on what version of i Tunes you are using. However, the song metadata at Music Brainz is pretty good and they have a cross-platform-ish ID3 editor called Music Brainz Picard that, with a plug-in called Cover Art Downloader, will grab covers for all your albums and embed them as needed.
You still need to delete cover art in Google Play to get the new art to update.
Compared to the previous app, Cover Art Grabber was able to fix more number of albums in the initial scan and displayed more number of search results for a particular keyword.
But it gave too many advert/promotional pop-ups while fixing the media which wasn’t a great feeling.
In researching this I found the latter method to be effective and sufficiently quick, but your mileage may vary.
Select all the songs in that playlist and delete the cover art as above.
Actually solve the problem: First, you need to edit the ID3 tags on your MP3s.
Removing just the bad album art: Create a playlist for albums with bad cover art.
Go to the Albums page and add the ones with bad art to the new playlist.