Pages from Comic Book Comics #3 by Fred Van Lente and Ryan Dunlavey. Fore more info, visit Evil Twin Comics.
So that's the secret origin of Roy Lichtenstein! That's how he created his artwork and how he developed a style that would become synonyms with the pop art movement.
The example provided above at least had some differences between the original panel and Lichtenstein’s final piece. Others, however, are much more egregious in their similarities, to the point that the only difference is the coloring. Take a look at this one for example.