The photo, which showed a man's bulging underwear, was sent from his Twitter account on Friday to a 21-year-old female college student in Washington State. His spokesperson said Weiner's Twitter account was hacked and calls the incident a prank.
"It was a hoax. It was someone sending a picture of a wiener on a Weiner's account. It's one of the jokes I've been getting since I was 5 years old. It's someone trying to cause mischief. It's someone trying to cause a distraction," he said in an interview.
The picture was quickly deleted but posted long enough for others to see. Weiner has more than 54,000 Twitter followers.
The congressman couldn't say with absolutely certainty that the person in the photo was not him.
"It certainly doesn't look familiar to me, but I don't want to say with certitude to you something I don't know to be the truth," he said. "I do know some certain truths here. I didn't send any Twitter picture. The person who allegedly it was sent to, this poor woman who was frankly a victim in all this, didn't get it."
The 46-year-old Democrat has been considering a run for mayor of New York City. He's known for his humor and sometimes combative style.
In a news conference Tuesday, Weiner didn't directly answer questions such as whether it was him in the photo or if he sent it. He got angry with reporters and even called one a "jackass."
He insisted that he wanted to move on from the incident, which was distracting from his work on Capitol Hill.
"I'm not going to talk about this anymore," Weiner told reporters on Capitol Hill. "I think that if I was giving a speech to 45,000 people and someone stood up and heckled in the back, I wouldn't spend three days talking to him. I'm going to get back to the conversation I care about."
The Associated Press contributed to this report.