Ever see a landscape scene and wondered where the photograph was taken? Researchers at Carnegie Mellon have devised the first computerized method to help answer your question.
It's a feat made possible by searching millions of GPS-tagged images in the Flickr online photo collection.
The algorithm, developed by computer science graduate student James Hays and Alexei A. Efros, an assistant professor of computer science and robotics, doesn't attempt to scan a photo for the obvious clues — such as types of clothing, the language on street signs or specific types of vegetation — as a person might do.
Rather, it analyzes the composition of the photo, notes how textures and colors are distributed and records the number and orientation of lines in the photo. It then searches Flickr for photos that are similar in appearance.
"We're not asking the computer to tell us what is depicted in the photo but to find other photos that look like it," Efros said. "It was surprising to us how effective this approach proved to be. Who would have guessed that similarity in overall image appearance would correlate to geographic proximity so well?"
Hays and Efros found they could accurately geolocate the images within 200 kilometers for 16 percent of more than 200 photos in their test set — up to 30 times better than chance. And even if their algorithm failed to identify the specific location, they often found that it could narrow the possibilities, such as by identifying the locale as a beach or a desert.
"It seems there's not as much ambiguity in the visual world as you might guess," said Hays, who recently presented the research at the IEEE Computer Society Conference on Computer Vision and Pattern Recognition in Anchorage, Alaska. "Estimating geographic information from images is a difficult, but very much a doable, computer vision problem."
Identifying the locale of a photo could enhance image search techniques, making them less dependent on captions or associated text. A computer system for geolocating photos could be useful in finding family photos from a specific trip and in some forensic applications.
Determining the location of photos also makes it possible to combine them with geographic data bases related to climate, population density, vegetation, topography and land use.