Other proposed types not currently approved or implemented:
The sleeve is the outer covering of a vinyl recording or compact disc, it is the paper covering closest in contact to the surface of the disc.
Use "inner" for the insides of a release if the packaging folds open (e.g. Digipak or some Double LP releases). Some compact disc releases use a transparent disc tray, use the "inner" type for scans of the image behind the tray.
Use "packaging" for pictures of an entire box set, usually these pictures include the outer packaging and the jewel boxes or other contents of the box. For example: http://www.discogs.com/viewimages?release=2943543
The inside of a folding CD cover (pages 2-3 of a standard 4-page inlay card). Often it replaces the booklet, sometimes it can be empty.
The back side of a front CD cover (folding or not folding) or of a booklet. It can be empty.
The unfolded front cover or booklet (front + front back). Sometimes the front cover is a part of an entire front full image, e.g.: http://img513.imageshack.us/img513/8739/500nf.jpg. Here the front is a right half of the front full.
The front cover of the boxed set of CD or LP albums.
The back cover of the boxed set of CD or LP albums.
The boxed sets have up to four designed spines.
Some CD and DVD releases have a designed external paper case. The design of this external case (front, back, spine) can be different to the one of the CD/DVD case, e.g.: http://img210.imageshack.us/img210/9996/extpapercase.jpg