Album covers are as much of an art form to graphic designers as the songs are art to the composer. When the two meet successfully the music actually seems to sound a little  better because together they become an experience.  With the advent of iTunes, album covers are not the double gate visions to behold that they once were. However, the cover is still integral to the branding of an artist across all media platforms and those artists are still very particular about how their image is presented to the public.

Album covers set the tone for a musical piece of work.
The artist works closely with the art director, photographer, and designer to get it just right because it is a record of time as well.