Meet the Greenhalghs, a family of English art forgers with an uncanny knack for researching long-lost pieces, duplicating them, and then convincing overeager art-types that their replicas were in fact the originals. For nearly two decades, living in "abject poverty" to protect themselves, the trio ran an art forgery ring—hinged on son Shaun's gift as a sculptor and painter—that had duped everyone from Scotland Yard to Sothebies. Make that the Art Institute of Chicago as well, which said Monday that it was in possession of a Greenhalgh-made Paul Gauguin, The Faun.

Several months ago, the family's luck ran out, leading to the imprisonment of Shaun and his mother, Olive. The Art Institutes's latest discovery may very well lead to revelations from other museums that they are in possession of Greenhalgh fakes.

Of course, hindsight is 20-20 for cops and art connoisseurs: "Looking at them now I'm not sure the items would fool anyone, it was the credibility of the provenances that went with them," one investigator said last month. But it was this sort of pomposity that drove the Greenalghs to believe they could deceive the art-world establishment. And for many years—and many millions—they did.