The British Broadcasting Corp. Monday said concerns had surfaced over the signature on the prints as well as some of the colors used.
Genuine Hirst prints can fetch around $18,656 (10,000 pounds) each, however forgers using modern copying technology have been drawn to his modernist works that make use of colored spots on grids, the BBC said.
Hirst is considered Britain's most famous living artist after David Hockney.
Sotheby's said the matter was under investigation.
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