For unknown reasons, the Music application on my Nokia N9 does not always display the album cover where expected. Instead, it displays the artist name and album title. Reports by other users of this phone suggest this isn't an uncommon issue, but offer no confirmed insight in the root cause of the problem unfortunately.

Fortunately, the symptoms of this problem are relatively easy to fix on a one-by-one basis.

In ~/.cache/media-art on the phone, copy the album art (in a JPEG file) to a file named using the following format:

album-$(echo -n "artist name" | md5sum | cut -d ' ' -f 1)-$(echo -n "album name" | md5sum | cut -d ' ' -f 1).jpeg 

Replace artist name and album name with the appropriate values for the album, in small caps (lowercase).

This follows the Media Art Storage Spec

Luckily, in most cases the above is not necessary and it suffices to store the cover picture as cover.jpg in the album's directory in ~/MyDocs/Music.