Peter Blake's collage for Sgt. Pepper's Lonely Hearts Club Band is one of the most celebrated, and iconic album covers of all time.
It's considered a work of art in its own right, but of course is constructed from copyrighted works by other artists, as well as with the creative input of Jann Haworth, Paul McCartney, Robert Fraser, and Michael Cooper.
Seems obvious (in hindsight) that the music on the platters would eventually utilise the same creative techniques as the sleeves that contained them - even if that hadn't been a direct consequence of the U.S. Government de-funding music education, and free instruments for schools in the late 70's, and early 80's (innovative kids figuring out how to use two turntables, a stack of funk records, and a microphone to create new forms of expression) - the technology quickly made it possible, and the chronically limited RAM capacity made it necessary.
It would be easy to dismiss both art forms as lesser, but I think the pictorial montage makes the process easier to relate to, and opens the door to considering the artistic process, the layers, and levels of thought that go into each carefully chosen reference, and the nebulous notion of truly original ideas / art - and in turn, hopefully gives people more to consider when tempted to simply dismiss collage in music.