They showed his daughter Laila, an investment lawyer with a practice in London, in a swimsuit and at her wedding, where alcohol was served.
"Such a campaign is the usual and only response of the regime towards whoever demands democracy, which is the only way for freedom and economic reform and social justice," ElBaradei told the newspaper.
An NDP spokesman said the publication of the pictures was "dishonourable."
"We in the National Democratic Party do not agree with this. Political disputes should never turn into personal attacks. It is dishonourable," said Ali Eldin Helal.
"This is not part of Egyptian culture. We are a culture that respects the privacy of families."
The pictures, insinuations of drinking alcohol which is forbidden by Islam and Laila's marriage to a banker in London with a non-Muslim name could raise eyebrows in increasingly conservative Egypt, where Muslim women largely dress modestly and cannot wed non-Muslim men.
But a senior Muslim Brotherhood official said the influential Islamist opposition movement was not interested in ElBaradei's personal life.
"We don't support any personality in particular. We agree on demands for reform and are part of a coalition that has people from different streams, including liberals," said Brotherhood politburo member Essam Erian.
"Of course they will have their own agenda and lives," he said. "Our priority is reform."
ElBaradei could not be reached for comment.
The former head of the United Nations International Atomic Energy Agency galvanised the country's opposition after he returned in February. His campaign says it has collected tens of thousands of signatures on a reform petition.
He initially received a hostile welcome from the government press, with a leading newspaper alleging he had Swedish citizenship and foreign support.
ElBaradei, 68, has ruled out running for presidential elections next year unless the constitution, which places restrictions on independent candidates, is reformed.
President Hosni Mubarak, 82, has not yet said whether he will stand again, but is widely believed to be grooming his son Gamal for succession.
Mubarak has ruled since 1981, and allowed limited political reforms over the past decade. He won the country's first multi-candidate presidential election in 2005 with a landslide.