I really like musicbrainz so far and I get a buzz when it finds gold matches along with image art. It is only these matches that I save and anything else is removed. My Library is so large that at the moment I want to get all the best stuff sorted first and sort other stuff later.
However I don’t know if this is the best way? I am going to have about a 3rd of music still without out cover art, what do people do if their is no cover art for the music they have?
In this case I use other sources like Discogs or Google picture search for such a cover.
If I find the exactly matching cover (including barcode, number of tracks, track titles, track order, release year, label etc.) I search the same release on MusicBrainz and add this cover for all other “fussy” users. 
I have been doing the same, It’s so laborious though. 
I am definitely picky about the data, but I think most people in MusicBrainz are, or they would be using FreeDB for all their information!
Over the years, I have had a few tracks go missing - not sure why, but I’m assuming it is because fsck fixed a problem and some of my files were victims. So, I have been re-ripping my collection over the past couple months.
I will take a stack of discs (~20 at a time) and rip them, tagging them only to exact matches. Surprisingly, I had to create several releases that I assumed would be in the system. I pull from CAA and fanart first, then the rest.
My second pass is to review all the cover images for the new rips. If any of them are missing or poor quality (which is probably under ~250x250 or just bad scans) I will then scan, crop, cleanup, color balance, and export as 1000x1000 (or wider) images. It makes me happy to see the beautiful scans once they are in the system, though! I have done about 300 scans so far. I even went so far as to determine the official dimensions for the CD inserts so that I could match the proportions exactly, although I have seen some slight variations in what I am scanning.
I’ve tried searching for images online, but really haven’t had much luck, so I gave up and do it myself.
The only tip I have is to do small batches at a time, otherwise it is overwhelming.
Good luck!
If you have trouble finding cover art, Album Art Downloader searches album art from a large amount of sources (including the Cover Art Archive). It’s mostly front images, but those are the most important ones anyway.
I guess I’m weird that I have CDs of almost all my music… so if there isn’t good-quality cover art already, I plop the CD in the scanner. Or for a few, in front of a digital camera (yeah for foil). Can certainly take a while, depending on the amount of art the album has, and how much of it needs high-resolution scans to descreen.
Low-resolution album art annoys me. Especially since I haven’t figured out how to tell Picard to ignore it yet, so I have have to wait until the edit to remove it applies, else I get both the low and high-resolution ones in the file.
PS: You can often get low-resolution artwork w/o uploading it by putting the ASIN (Amazon item number) on the album, then cover art will be pulled from Amazon. This also has the advantage of not getting in the way of a later high-resolution upload.
It is a hassle, but those few minutes work on your behalf will save potentially thousands of users the same trouble later on! So a massive thanks to all who take the time to put up good quality cover art!
Album Art Downloader looks like a great help - I’ll have to play with it to see what I can find - thanks!
That’s dedication. 
Sounds about right! Though 20 at a time… wow, that’s a lot of work!
Also, when ripping I use morituri which verifies the rip against an accuraterip database. Which, it seems, is sparsely populated w/r/t a lot of the classical releases I’m ripping. So a bunch I wind up re-ripping on a second CD drive to make sure I get the same result.
I store all the stuff in git-annex, sync’d to several machines, to make sure none of it gets lost.