So i was playing a flac album and noticed that album artwork wasn't working when playing it by the cue (so you can get the track details, btw probably my fav feature in Cog). I normally see album artwork as part of the Growl notifications.
I took a quick look at the source. The reason for this is because you use the CueSheetMetadataReader instead of TagLibMetadataReader. That makes sense since cues contain the data that the files normally dont contain in them. Problem is, the artwork extractor that you wrote was added on top of the TagLib interface, not the common reader. As such the CueSheet stuffs doesnt get parsing for artwork coming from files in the same directory (like "cover.png", etc.)
I've attached a quick hack that basically copies and pastes the cover file looker-uper from TagLibMetadataReader, but ideally these methods should be moved out of both and into a non-Plugin.