1. A computing device for automatically identifying portions of an image of a physical scene as depicting physical objects of predefined types in the physical scene, the computing device comprising: one or more processing units; and computer-readable media comprising computer-executable instructions, which, when executed by the one or more processing units, cause the computing device to: generate a set of image features from two-dimensional image data that was obtained by two-dimensionally imaging the physical scene; generate a set of geometric features from three-dimensional image data that was obtained by three-dimensionally measuring the physical scene coincidentally with the two-dimensional imaging of the physical scene; generate correspondences between image features in the generated set of image features and geometric features in the generated set of geometric features; identify, based on a first subset of the image features, a first portion of the image of the physical scene as depicting a physical object of a first predefined type; select a first subset of the geometric features that corresponds to the first subset of the image features based on the generated correspondences; and determine, based on the first subset of the geometric features, that the identified first portion of the image does not actually depict a physical object of the first predefined type.