Caterina Fake knew she was onto something when one of the engineers at her Vancouver, British Columbia-based online game start-up created a cool tool to share photos and save them to a Web page while playing.
"It turned out the fun was in the photo sharing," she says.
Fake scrapped the game. She and her programmer husband, Stewart Butterfield, transformed the project into Flickr. In less than two years, the photo-sharing site - now owned by Internet giant Yahoo - has turned into one of the Web's fastest-growing properties.
"Had we sat down and said, 'Let's start a photo application,' we would have failed," Fake says. "We would have done all this research and done all the wrong things."
Fake and Butterfield's company, Ludicorp, never did launch a game. Yahoo bought the company in March for an undisclosed sum and moved the 11-person team to Yahoo headquarters in Sunnyvale.
Since then, Flickr has been on a roll, riding the wave of consumer fascination with digital cameras. Shutterbugs are less likely to make many prints these days but still want an outlet to show off their work.
That's where a free, ad-supported site such as Flickr comes in.
Flickr's traffic grew 448% to 3.4 million from December 2004 to December 2005, according to Internet measurement firm Nielsen/NetRatings. In the nearly 12 months since Yahoo purchased it, the site went from 250,000 registered users to more than 2 million. About 100 million photos have been posted at the site.
Chad Hurley, CEO of video-sharing site YouTube, is a Flickr fan. He says the site has resonated so quickly with the public "because it brought innovation to a problem people thought was already solved - how to share photos online."
Flickr's snazzy photo-sharing features set it apart from the dozens of other photography sites. Friends can check out newly posted pictures via searching and add their own "notes" to photos they like.
One distinctive tool lets bloggers simultaneously post photos on their own blogs and at Flickr.
It also uses a tool called "tagging" - adding a few words of text to each posted photo - so that a picture can be easily searched online.
Trip Hosley, co-owner of San Francisco club Shine, became a fan after his brother, Nate, became a father for the second time and tagged pictures of the newborn "Deuce" at the Flickr site. "Within an hour of the birth, there were 100 pictures online that all our family and friends could see, instantly, just by searching for 'Deuce,' " he says.
Hosley even installed a photo booth at Shine where patrons can sit and snap their own pictures and have them instantly uploaded to Flickr.
Yahoo bought the company as much for Fake and Butterfield as it did to land Flickr, says analyst Charlene Li of market tracker Forrester Research.
"Caterina is very dynamic, smart and energetic, and her job is to help Yahoo with the social tools," Li says. She calls Butterfield "a brilliant programmer."
Butterfield says Flickr's biggest innovation came from recognizing the social nature of photography.
"It's meant to be shared, talked about, pointed to, saved, archived and available by as many means as possible," he says.
Yahoo has two photo-sharing sites, Flickr and the more traditional "share-and-buy-prints"-oriented Yahoo Photos.
But Yahoo executive Bradley Horowitz, the head of technology development, says there's room at Yahoo for multiple areas of photo sharing, just as it offers instant messaging and e-mail as two different communication tools.
Yahoo has kept the Flickr site low-key, with no front-page promotion. Word of mouth is its best marketing tool, Horowitz says.
"The right way to find Flickr is to be invited by a friend, to get plugged into the social network that way," he says. That way, you're more likely to "get it," he says.
Flickr has a spare, hip look that displays photos larger and more stylishly than many others but isn't as simple to navigate as competitors such as Shutterfly and Kodak EasyShare Gallery.
It uses terms such as "photostreams" to describe personal photo collections, "interestingness" to describe cool new pictures and "sets" to describe groups of photos.
There is no simple tool to share pictures via e-mail. Instead, Flickr users must copy the Web address Flickr assigns to the photos into an e-mail.
It's a deliberate omission. "With the kind of growth we've experienced, we're not sure our servers will be able to handle the onslaught from an e-mail application," Fake says.
She says an e-mail function is coming soon: "We know people really want it, we just want to make sure we're prepared."
For now, Flickr users seem untroubled by the lack of a one-click e-mail feature. Ricky Fisher, a Seattle graphic designer, simply shares his pictures with others via the Flickr Web address. What he likes most about the service is its international flavor; he checks out interesting photographs from all over the world.
At the bottom of Flickr's home page are four thumbnail images of the most recently uploaded pictures from the Flickr community. Fisher watches the page to see the new photos and reaches out to photographers whose work he admires.
"You see a lot of amazing stuff this way," he says.