From Albums context menu or from the Songs Editor you can invoke the Cover Editor to search the album cover on the Web. In the Cover Editor you can redefine the name of the artist or the album name to make refine the search. You can select the online cover search engine (Apple or Last.fm). The Search again button repeats the cover search with the current texts (same as pressing Enter in them).
Once you have found a cover you like, to save it you can double click it or press ‘OK’. If the Cover Editor was invoked from the context menu, the cover will be saved on the album directory using as name the first entry on ‘Words to detect covers’ from the Library section of the Preferences. But If it was invoked from the Track editor, it will be embedded into the file instead.