1. A method comprising: receiving a two-dimensional image to be converted to a first three-dimensional image; identifying, in a data store, a second three-dimensional image that corresponds to a stereoscopic pair of images and is visually similar with the two-dimensional image to be converted, wherein the second three-dimensional image was previously created from a conversion of another two-dimensional image or was initially captured as a three-dimensional image; computing, by a processing device, a feature-to-depth mapping function for the first three-dimensional image by averaging depth values of at least a portion of a plurality of pixels from an approximate depth map associated with the previously created second three-dimensional image that corresponds to the stereoscopic pair of images and is visually similar with the two-dimensional image to be converted; applying the feature-to-depth mapping function to a plurality of pixels of the two-dimensional image to determine a depth value for each of the plurality of pixels; and generating the first three-dimensional image based on the depth values for the plurality of pixels of the two-dimensional image.