I'm using almost all lossless, being on a Mac, that's ALAC by default, but I converted a number of files to FLAC (similar issues) before the new version with ALAC/AAC support became available. I embed all my artwork at the same size 600x600 semi-manually, and I can verify it by looking at the filesystem, which doesn't use a database or cares about cover art in the folder, it's in each individual track, if not, the thumbnail would show a generic icon.
Opening it in 3 different players besides iTunes, all of which do NOT share any kind of cover art database, plus a dedicated tagging app: the covers appear for each individual track as well. (I'd also mention my iPods, but since they tie into iTunes, it'll be taken care of no matter what anyway.)
I even tested a couple of the ones with issues independently in Windows (and not iTunes either), again no problem displaying the cover for each individual track... the only one it doesn't work on is the AK100?!?
If the size was an issue, then why is it working for a few that I absolutely know has the art at 600x600px because I scaled it myself? I thought maybe PNG vs JPG, but they are all JPG. That's what makes the issue so frustrating: what is the cause? Not that a decent codec implementation should have these issues...
Edited by TheGrumpyOldMan - 1/26/13 at 11:04pm