"Swipes" are comic book panels that were obviously copied from another source, but not credited. They are pretty common. It's a fun pastime for comic book fans to identify swipes. Unlike plagiarism, people don't really think the "swiper" is much of a cheat. I'm not sure why, but I sort of agree with that sentiment. I don't think badly about a comic book artist who swipes occasionally but I do think badly of a writer who copies someone else's writing.
Here's an interesting swipe discovery: Bob Kane, the creator of Batman, swiped an illo from a 1938 issue of a pulp magazine called Gang Busters In Action for the Batman story in Detective Comics #33 (November 1939.) Check out the fingers of Bruce Wayne's left hand. They are green in the panel, but should have been skin colored.
Link (Thanks, Eric!)