This (dirty, dirty) script will help manage album art images between your music library and portable device(s). 

It assumes that your album art images are all named something common (my default is folder.jpg) and that your portable device supports album art images of a certain name (my cowon d2 looks for cover.jpg).

Uses ImageMagick and the quick_magick gem to do the actual image creation. Uses SQLite3 and the gem to keep a table of SHA1 hashes of music files and album art images in the music library.

config.ini has the following options:
localDir = folders in local music library, separate folders using |
destDir = folders on portable device(s), separate folders using |
musicTypes = music file types to look for, separate using ,
imageTypes = local album art image file types to look for, separate using ,
originalName = file name of local album art images
coverWidth = image width of cover image to be generated
coverHeight = image height of cover image to be generated
coverType = image file type of cover image to be generated
coverName = file name of cover image to be generated