The photo, which shows a man's genitals, was published by a website after conservative blogger Andrew Breitbart showed it to the hosts of Sirius XM radio's Opie & Anthony Show.
Separately, officials say Weiner's wife, Huma Abedin, is pregnant. A spokesman at the State Department, where she is a top aide to Secretary of State Hillary Rodham Clinton, had no comment, but several Democrats said the couple had told their friends.
Weiner is facing calls for the first time for his resignation from Democrats, led by Rep. Allyson Schwartz of Pennsylvania.