The U.S. Federal Bureau of Investigation (FBI) arrested two Michigan residents on 2 December (09) after they allegedly threatened to release the snaps of the ER star unless he handed over $680,000 (£425,000).
Stamos went to authorities and helped them snare alleged extortionists Allison Coss, 23, and Scott Sippola, 30, in a sting, according to an affidavit obtained by The Smoking Gun.
According to the document, the actor attended a Florida party in 2004 with Coss and her pal when the pictures in question were taken. He received an email in November (09) from an unknown source threatening to "harm (Stamos') reputation" by releasing the shots to the media, at which point the star's lawyer contacted the FBI.
But Stamos' rep has stepped in to clarify the nature of the images: "The photos in question are photos of John posing with fans. At the conclusion of the investigation and hearing, the photos will be available and the public will be able to see that the photos are simply John posing with fans."
Coss and Sippola were released on bond on 3 December (09). The case is still pending.