Slight OT, but this is perhaps one of the only criticisms I have with calibre as this too was not very clear to me, and I have a good deal of expertise with metatags/covers from audio stuff.
Wishlist for calibre:
- maybe a button on the metatag editor page that says "insert this cover" for XYZ format? And then confirm? Click, bang, cover inserted. No need to do any conversions.
This prolly has been asked for before I would think...