In the competitive world of Washington protests, crowd size is often a matter of dispute. Organizers usually boast of huge crowds, while police and the news media offer much smaller estimates.

So supporters of Saturday’s “tea party” protests against President Barack Obama were quick to highlight their big turnout. To bolster countless claims on blogs and Facebook, many posted a photograph that showed a gargantuan crowd sprawling from Capitol Hill down the National Mall to the Washington Monument.

But it turns out the photo is more than 10 years old, apparently taken during a 1997 Promise Keepers rally.

On Saturday, estimates about the crowd spread quickly through the conservative blogosphere. Many writers, including author Michelle Malkin, pegged the number of people between 1 million and 2 million. Those reports were largely based on information from people in the crowd.

Malkin, for example, updated her blog at 12:34 p.m. noting that, “Police estimate 1.2 million in attendance. ABC News reporting crowd at 2 million,” and she cited a Twitter post from Tabitha Hale, writer of Pink Elephant Pundit, who was in Washington for the protest.

Many bloggers said the media was unfairly reporting much smaller numbers, and many included the photo.

“I have no doubt that Washington Democrats are well aware of how many people turned out, even as their media outlets try to downplay the event,” said Power Line, a conservative blog that linked to the photograph from Say Anything , another conservative Web site.

“ 'Media’ estimates range from 60,000 to 500,000 to around 2 million (yes, 2,000,000),” wrote John G. Winder for the conservative blog Cypress Times. “Those estimates, the language employed, and the visuals chosen for use in reporting the rally and representing the people gathered, vary greatly based solely on bias.”

In the mainstream media, crowd estimates varied.

The New York Times reported that “thousands” of protesters “filled the west lawn of the Capitol and spilled onto the National Mall,” while Fox News wrote that “tens of thousands” marched on Washington. CNN said “reporters at the scene described the massive crowd as reaching the tens of thousands.”

Pete Piringer, public affairs officer for the D.C. Fire and Emergency Department, said the local government no longer provides official crowd estimates because they can become politicized. But the day of the rally, Piringer unofficially told one reporter that he thought between 60,000 and 75,000 people had shown up.

“It was in no way an official estimate,” he said.

We asked Piringer whether there were enough protesters to fill the National Mall, as depicted in the photograph.

“It was an impressive crowd,” he said. But after marching down Pennsylvania Avenue to the Capitol, the crowd “only filled the Capitol grounds, maybe up to Third Street,” he said.

Yet the photograph so widely posted showed the crowd sprawling all the way to the Washington Monument, which is bordered by 15th and and 17th Streets.

There’s another problem with the photograph: It doesn’t include the National Museum of the American Indian, a building located at the corner of Fourth Street and Independence Avenue that opened on Sept. 14, 2004. (Looking at the photograph, the building should be in the upper right hand corner of the National Mall, next to the Air and Space Museum.) That means the picture was taken before the museum opened exactly five years ago. So clearly the photo doesn’t show the “tea party” crowd from the Sept. 12 protest.

Also worth noting are the cranes in front of the Smithsonian Museum of Natural History. According to Randall Kremer, the museum’s director of public affairs, “The last time cranes were in front was in the 1990s when the IMAX theater was being built.”

It appears that the photo was actually taken in 1997 at a rally for Promise Keepers, a group for Christian men. According to the group’s Web site, nearly 1 million people attended the event. Photos of the Oct. 4, 1997, event that were posted on various Web sites in 2003, 2008 and earlier this year show either the same picture or a similar photo that has identical tents and what appear to be TV screens in the same locations.

Conservative bloggers who originally posted the picture have backed down.

Malkin, like some of her conservative cohorts, retracted the number she had attributed to ABC when the network chastised FreedomWorks president Matt Kibbe, whose organization arranged the event, for inaccurately telling the crowd that the news organization had reported the crowd at 1 million to 1.5 million people.

Malkin linked to the ABC story on her site, and changed her blog post headline to “Celebrating the 9/12 rallies; Turnout estimated at 2 million; Update: How many?; FreedomWorks in error.”

Say Anything updated its original post to say that the picture was “of the wrong rally.” An accurate photo “clearly shows that (the rally) didn’t take place on the mall nearly as extensively as the image I mistakenly posted does.” Power Line took the picture down all together.

But because mistakes can still live forever on the Internet and many people who saw the photo on Facebook were unaware it was found to be the wrong picture, we decided to still rate it on the Truth-O-Meter. And Pants on Fire it is.

UPDATED: We updated this item with new details about the Promise Keepers photos.