Select the songs and click "Get Song Information" will get info from gracenote:



If some info cannot be got from gracenote, e.g. album cover, you could search and download it from the website, and then click "Change Cover" to add it in MediaHome:




Or just change the album cover if you think the current one is not good:




Please note: 

These formats are supported to be added cover: mp3, mpa, aiff, flac, etc.

Other formats, e.g. AAC file is not supported to add album cover to.