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Flickr - whose motto is 'Share your photos, Watch the world' - is hoping to distinguish itself from all of these with what is arguably an even greater ambition: to become the largest and most easily searchable repository for the world's photographs.

Two months ago it introduced a feature called Places, which allows users to conduct in-depth searches for photos by location. The idea is that, as more and more cameras have GPS-based features, which allow users to pinpoint the exact location a picture is taken before they upload it to the web, new revenue streams will open up.

So-called 'geo-targeted' ads, much like the ones the web-based mapping services like Multimap are trying to introduce, have long been flagged as an opportunity. (Chances are if you're looking for a photo of the Maldives, you might like to see an advert for a hotel there.) Butterfield maintains for the moment, though, that "if you divide the world into 50 square metre chunks, there simply aren't enough advertisers per chunk that want to take advantage of it.")

Then there is the scope - as Flickr continues to grow - to facilitate the trade of photos in its database. (Virgin, for instance, is one of several companies to have sought the rights to use a Flickr photo in an advertising campaign.)

Giving the clearest indication yet that the site may move in this direction, Mr Butterfield says: "Removing some of the friction so that people can more get connected with a photographer they find on Flickr and buy the rights to their pictures - that would definitely be good."

According to Jon Gibs, an analyst at Nielsen, Flickr is unique among photo-sharing sites because the photos in its database are connected up in such a way that adds value for the end user, the new Places feature being an example.

"The depth of content really isn't rivalled, and the fact that users are now tagging all their pictures (by location) will lend itself to amazing targeting."

The trick, he says, will be in knowing how to make money out of it while having due regard for users' privacy. "It's the Facebook conundrum," he says, referring to the networking site's recent decision - following enormous protest - to change a feature that would have publicised users' online activities to their friends without consent.

"You have this incredible depth of content, but you want to be able to monetise it without scaring the hell out of everyone."

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