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New geotagging method draws on Flickr photos

Adding location information to photos is hard. Carnegie Mellon has found an easier way: compare your photo with similar ones on Flickr that already are geotagged.

IM2GPS compares a sample photo (top left) to geotagged Flickr photos to find other similar shots (top right) to guess where the sample was taken.
IM2GPS compares a sample photo (top left) to geotagged Flickr photos to find other similar shots (top right) to guess where the sample was taken. Carnegie Mellon University

Thousands of others have taken the trouble to geotag their photos, so why should you have to jump through a lot of technical hoops to add location data to your pictures?

That's the upshot of a technique devised by Carnegie Mellon researchers and announced Wednesday. The technique, called IM2GPS, compares a single photo to the millions already on Flickr that already have latitude and longitude coordinates.

The algorithm looks at a photo's properties, such as textures, color distribution, and line patterns, then looks for matches at Flickr.

"We're not asking the computer to tell us what is depicted in the photo but to find other photos that look like it," said Alexei A. Efros, assistant professor of computer science and robotics, in a statement.

Efros also has been involved in photo research such as the scene completion technology that can patch over unsightly elements in a photo by drawing from similar ones stored at Flickr.

The researchers found they could locate sample photos within 200 kilometers for 16 percent of their test photos, which may not sound terribly useful, but it is 30 percent better than chance would predict, the university said. And that could still be useful for tasks such as forensic crime research or for guiding other image-processing tasks--for example identifying a taxi in Japan.

It worked more specifically at times, for example matching Paris' Notre Dame cathedral well, but the algorithm found Sydney's Opera House similar to a hotel in Mississippi and to a bridge in London.

Geotagging today is a complex task that typically requires a user to run specialized software that pulls location data from a GPS device's track log, then adds it to photos depending on the time each was taken. Geotagging isn't for the faint of heart today, though higher-end cameras from Canon and Nikon make it easier with the ability to plug a GPS directly into the camera, and camera makers have begun building GPS into some models.

Geotagging may seem abstruse, but it has potential advantages. You could find out just where that photo of the nice church in Ireland was taken even long after your vacation itinerary has faded from memory, for example.

Or with technology that converts geographic coordinates into actual place names, you could find your own photos or others' shots with ordinary search terms. For that latter challenge, Flickr is working to try to make it easier for users to identify in works the locations of their geotagged photos.