Mp3Tag supports only "Cover (front)" as the picture type and no description of the picture. It would be nice to have full compatible support for embedded FLAC pictures, i.e. a drop-down list for the picture type and a text box for the description at the extended tag dialog window.
PS: make it optional to use the picture type and/or the description as the default name when saving the image. So when people use short and logical description of the CD artwork scans in the description field, for example "tray", "cd", "label", "booklet 01", "booklet p02-p03", etc it can be easily used to name the files correctly.