This is NOT AN ENTRY, since it's not a cover. But this topic demands that someone post Roy Lichtenstein's (in)famous painting "WHAAM!", which is on permanent display at London's Tate Gallery:
This painting was "inspired" (i.e., pretty much "appropriated") from a splash panel drawn by Irv Novick in DC's All-American Men of War #89 (February 1962):
Note that it wasn't a total swipe, since Lichtenstein made some changes to the attacking aircraft. He did this by being "inspired" by a panel drawn by Jerry Grandenetti in the very next issue of that same comic: