Peter Belhumeur just wanted to know what type of tree was outside his apartment. He scanned field guides, looking for willowlike leaves with a wavy, spiked edge, but he couldn’t find the right one. Neither could his neighbors.
As it happened, though, he was building a tool designed to address just this problem. Belhumeur is a computer scientist at Columbia University who has worked on face recognition, and he and David Jacobs of the University of Maryland in College Park had dreamed up an iPhone app that would use similar mathematical methods to recognize trees. Leafsnap (www.leafsnap.com) allows a person to pick a leaf from the U.S. Northeast, snap a picture of it against a white background, and find out which tree species it is most likely to have come from.
“We thought we could build an electronic field guide for the 21st century,” Belhumeur says, “so that the search would be initiated by an image,