cannot copyright style. Most of the comic artists didn't know Lichtenstein used their work until they were contacted by the documentarian. Comic book artist steal or as they say "swipe" from each other constantly - maybe that's one reason the Publishers never sued - they didn't want to open up that can of worms.
check out these "swipes"
forum.cbcscomics.com
Those could be considered stealing, comics taken and used in another comic. What Lichtenstein did is more accurately called "appropriation". He took one thing and then used it for a different purpose.
Where I have trouble is stuff like this:
View attachment 29868
So, you can never create an image of a girl with her hands crossed, elbows leaning on a table. I would say it was "inspired', not appropriated. Definitely similarities to this random frame among hundreds of frames from an obscure comic book - but if this one is stealing, then what about the ones of a guy opening a door or sitting in a chair? If this image was famous, or if the pose, or setting was unusual etc. then a case might be made - in my opinion.--otherwise --