http://forums.musicbrainz.org/viewtopic.php?pid=21191

That thread describes how Picard will attempt to embed a 16-MB cover art file into FLAC, and fail.

I don't know if the solution is to fix the FLAC encoding, or if it's simply not possible to do this in FLAC.

It would probably be better to limit the size of embedded cover art anyway. ( PICARD-237 ) but if it is made optional, this problem still needs to be fixed.