From Open Culture:
The Cover Art Archive, a joint project of the Internet Archive and MusicBrainz, an “open music encyclopedia that collects music metadata and makes it available to the public.
The collection now numbers in the several hundred thousands—upwards of 800,000, according to its results counter—but some of the uploads are not yet complete with images. You are invited to contribute and help make this amazing resource even more comprehensive.
“To get started,” the MusicBrainz blog writes, “log in with your MusicBrainz account (or create a new one) find your favorite release and then click on the cover art tab to view the existing pieces of art and/or upload new ones.”
The Cover Art Archive is a joint project between the Internet Archive and MusicBrainz, whose goal is to make cover art images available to everyone on the Internet in an organised and convenient way.
Images in the archive are curated by the MusicBrainz community and go through a peer review process to ensure that they are correct, free of spam and of the best quality. If you would like to contribute cover art, create a MusicBrainz account and follow the guide.
MusicBrainz also provides API documentation for retrieving cover art via a release MBID. If you have any questions regarding the images in coverartarchive.org, please email info [at] archive [dot] org. All images are fair use and free to download or participate in the program.
Visit Cover Art Project Online: https://archive.org/details/coverartarchive&tab=collection
Examples of Cover Art: