1. A computer-implemented method, comprising: obtaining, by a computer system, an image that was captured by a computing device; identifying, by the computer system, image characterizing data for the obtained image, the image characterizing data identifying characteristic points of one or more items in the image; obtaining, by the computer system, general device position information that indicates a geographic location at which the image was captured by the computing device and that was generated using information sensed by one or more position sensors of the computing device that sense geographic location information; selecting, by the computer system, a plurality of geo-coded images based on the general device position information; comparing the image characterizing data for the obtained image with image characterizing data for the plurality of geo-coded images; determining, by the computer system and based on a result of comparing the image characterizing data for the obtained image with the image characterizing data for the plurality of geo-coded images, calculated device position information that indicates a refined geographic location at which the image was captured by the computing device; and providing, by the computer system and to the computing device, calibration data for causing the computing device to calibrate, based on the calculated device position information, the one or more position sensors of the computing device that sense geographic location information.