Indeed, geotagged Flickr photos could contribute to a project from Microsoft Research and the University of Washington, in which researchers have developed an algorithm that can stitch together disparate photos to create a seamless virtual tour of places like the Eiffel Tower in Paris. A collection of accurately geotagged photos from Flickr could benefit this project, says Suman Nath, a Microsoft researcher who works on a real-time mapping project called SenseWeb (see "Microsoft's Plan to Map the World in Real Time"). Pictures that have the same geographic location can be manipulated by algorithms that "merge those images," he says. "You can make a three-dimensional tour using all that information."

Privacy issues remain a concern, however, with the increasing popularity of geotagging. Flickr's Butterfield and his team have added some features to allow varying degrees of disclosure for pictures and geographical information. For instance, pictures can be either publicly visible or viewable only by some people. Additionally, a person has to actively add a geotag, and it can be private even if the picture itself is public. "One of the aspects of this that we've thought quite a bit about is privacy," Butterfield says.

The Flickr team is looking for ways to improve other aspects of the service, too. For example, with a time-based search, people can look for pictures taken on a specific day, or images of a location taken at different times of year. And, as Yahoo improves its maps, geotagging through Flickr will become more feasible in places outside the United States.

Butterfield predicts that geotagging will continue to gain momentum as more cameras and camera-equipped cell phones come with global positioning systems that automatically tag a picture with its longitude and latitude. In addition, he says, software developers and cell-phone service providers are making it easier to share photos and upload them to the Internet. "In many ways we're on the edge," he says. "Over the next couple of years, we'll see a lot more connectivity."