(CNN) - Cindy McCain, the wife of the 2008 Republican presidential candidate, has posed for a Web site promoting same-sex marriage.
McCain, who's married to Arizona Sen. John McCain, appears in a photograph on the site with a piece of silver duct tape over her mouth and the slogan "No H8" written on her cheek.
The site's owners were stunned when Mrs. McCain came to them with the idea of posing for them, they said when posting her photo Wednesday.
"We've often been surprised at some of the different individuals who have approached us showing their support. Few, though, have surprised us more than Cindy McCain," wrote Adam Bouska and Jeff Parshley.
"The McCains are one of the most well-known Republican families in recent history, and for Mrs. McCain to have reached out to us to offer her support truly means a lot," they wrote.
"Cindy McCain wanted to participate in the campaign to show people that party doesn't matter - marriage equality isn't a Republican issue any more than it is a Democratic issue," they argued, saying it was "about human rights."
The McCains' daughter Meghan, a vocal supporter of same-sex marriage, also appears on the site.
"I couldn't be more proud of my mother for posing for the NOH8 campaign. I think more Republicans need to start taking a stand for equality," Meghan McCain wrote on her Twitter page.
Meghan McCain appears holding an elephant - the symbol of the Republican party - with tape over its tusks.
Running for president, John McCain said he believed marriage should be between one man and one woman.
He reiterated that view through a spokeswoman Thursday.
"Senator McCain respects the views of members of his family. The senator chaired the effort to successfully pass Arizona Proposition 102, the Marriage Protection Amendment, and his opposition to gay marriage remains the same," Brooke Buchanan said.
The No H8 campaign arose in response to California's back-and-forth on same-sex marriage - first approved by the courts, then overturned by voters in a statewide referendum called Proposition 8. The issue is back in court now.
Bouska, a photographer, launched the site with Parshley "as a silent protest," they wrote.
It showcases pictures of Californians who oppose Proposition 8, they wrote when it launched nearly a year ago. It expanded to include celebrities and other supporters of same-sex marriage, all appearing with duct tape over their mouths and "No H8" painted on their cheeks.