Dave Arnold told Fox News in an email that the tweet, directed at a woman, was "a distraction" from the married New York Democrat's "important work representing his constituents."
"Anthony's accounts were obviously hacked," Arnold said. "He doesn't know the person named by the hacker, and we will be consulting on what steps to take next."
The photo showed a man's bulging underpants.
It first was reported Saturday by BigGovernment.com, a website run by conservative commentator Andrew Breitbart. The site said the photo was tweeted to a Seattle woman.
The photo was quickly deleted.
Gennette Cordova, the woman who received the photo, released a statement to the New York Daily News saying this wasn't the first time she received lewd messages from the person who hacked the congressman's account.
"The account that these tweets were sent from was familiar to me; this person had harassed me many times after the congressman followed me on Twitter a month or so ago. Since I had dealt with this person and his cohorts before, I assumed that the tweet and the picture were their latest attempts at defaming the congressman and harassing his supporters," she told the New York Daily News.
Cordova clarified to the paper that she has never met the New York representative or talked to him.
"There have never been any inappropriate exchanges between Anthony Weiner and myself, including the tweet/picture in question, which had apparently been deleted before it reached me."
Cordova added that she is a 21-year-old college student from Seattle, and while a fan of Weiner, her twitter commentary on him were merely jokes.
"Contrary to the impression that I apparently gave from my tweet, I am not his girlfriend. Nor am I the wife, girlfriend or mistress of Barack Obama, Ray Allen or Cristiano Ronaldo, despite the fact that I have made similar assertions about them via Twitter," she wrote, according to the New York Daily News.
Weiner later joked about the account hacking on Twitter, asking whether his kitchen blender would be next to "attack" him.
Weiner represents New York's 9th District, which covers parts of Queens and Brooklyn, where he was born and raised. He failed in a 2005 bid for the Democratic nomination for mayor of the city but still is widely considered a contender for the office.
He has worked on issues including public housing, homeland security and energy for his constituents.
Weinger, 46, is married to Huma Abedin, an aide to Secretary of State Hillary Clinton.
The Associated Press contributed to this report.