How do I make Banshee re-scan for cover art?
Solution 1:
Try typing in a terminal:
banshee --fetch-artwork
This will make banshee download missing covers.
Solution 2:
The covers are stored in ~/.cache/media-art/ You might try renaming the folder to force Banshee downloading the covers again. I haven't tested the solution, so don't delete the folder alltogether.
Solution 3:
Banshee stores album covers in ~/.cache/media-art. If you copy that folder along with the others, the covers should all be waiting for you when you open up Banshee.