Speaking at a packed press conference at Moorabbin on Tuesday morning, Riewoldt said the photo was taken by teammate Sam Gilbert on a holiday to the United States last year.
Photos were loaded onto Gilbert's computer and were alleged to have been obtained illegally.
The photo of a nude Riewoldt with teammate Zac Dawson and another explicit photo of Nick Dal Santo were then uploaded to a young woman's Facebook profile page on Monday.
Flanked by St Kilda CEO Michael Nettlefold and coach Ross Lyon, Riewoldt said he could not understand the reasons for posting the photos and that he would explore his legal options in the coming days.
"As a professional AFL footballer, I pride myself on the role that I undertake at the St Kilda Football Club as its captain and the personal satisfaction I have gained by dedicating myself to this great sport for in excess of 10 years at the highest level," Riewoldt said.
"Given that I have had absolutely no association with this person at any point in my life, I am at a loss to understand what their motivation could possibly be."
Riewoldt was made aware the photos were circulating several weeks ago by his player manager Ricky Nixon but did not see the image until yesterday.
He said he was "bitterly disappointed" the image remained on Gilbert's camera after his teammate took the photograph in a Miami hotel room late last year.
"I asked Sam to delete the photo; it was my understanding that it was deleted," he said.
"To infer that I would stand there and pose for a photograph naked, knowing it was going to be kept is absolute garbage for people to think that."
The Saints captain scoffed at suggestions he shared part of the blame for allowing the photo to become public.
"When I'm in a private hotel room and I'm with friends and a friend takes a photograph and I ask them to delete it, I think it is reasonable to assume that would be the case and it wouldn't turn into something like this, " he said.
Dal Santo was not at the press conference but Nettlefold said he remained in good spirits despite the violation of privacy.
"Nick Dal Santo's position is identical to Nick Riewoldt's position," Nettlefold said.
"Nick Dal Santo has never met and does not know the person who posted those photographs.
"We understand that was taken from Sam Gilbert's computer as well."
