You're recalling iTunes Match, the service which allows you to upload/match your iTunes library and access it across multiple devices. This service is $25/year.
However, you can have iTunes download album art (even for albums you've imported and haven't bought through iTunes) for free. You can just select every song in your library and the right-click and choose "Get Album Artwork" or something like that. It works decently for music you have somewhat accurately tagged (at least a correct artist and album name). Again, this fails for a lot of electronic music though.
"Again, this fails for a lot of electronic music though."
It also fails for classical music. But since I ripped CD's I just scanned in the cover and added the art. Trust me, it was time consuming. But there is hope, iTunes has added much more classical/opera recently. So changes are, if I had to do this all over - a lot of the art would be available from iTunes.
In my collection, The album art matcher is quite bad. Stuff that's tagged correctly and well known (e.g. Led Zeppelin) comes up with the wrong (but related) image. Where it really falls down are compilations, I think it's running about a 20% hit rate on those.
However, you can have iTunes download album art (even for albums you've imported and haven't bought through iTunes) for free. You can just select every song in your library and the right-click and choose "Get Album Artwork" or something like that. It works decently for music you have somewhat accurately tagged (at least a correct artist and album name). Again, this fails for a lot of electronic music though.