13. A computer-implemented method, comprising: determining a plurality of semantic category scores for a digital image via application of a corresponding plurality of classifiers; and automatically determining a semantic category profile for the image based on the plurality of semantic category scores, wherein the semantic category profile characterizes semantic content of the image, and is useable to perform semantic based operations with respect to the image; analyzing a plurality of semantic categories with respect to a plurality of digital images based on one or more criteria, wherein the one or more criteria comprise at least one of: relevance of each of the semantic categories; consistency with human based classification; or accuracy of each of the semantic categories; and automatically performing: determining a subset of the semantic categories that efficiently spans the semantic content of the plurality of digital images based on said analyzing; or ranking the plurality of sets of semantic categories based on said analyzing.
13. A computer-implemented method, comprising: determining a plurality of semantic category scores for a digital image via application of a corresponding plurality of classifiers; and automatically determining a semantic category profile for the image based on the plurality of semantic category scores, wherein the semantic category profile characterizes semantic content of the image, and is useable to perform semantic based operations with respect to the image; analyzing a plurality of semantic categories with respect to a plurality of digital images based on one or more criteria, wherein the one or more criteria comprise at least one of: relevance of each of the semantic categories; consistency with human based classification; or accuracy of each of the semantic categories; and automatically performing: determining a subset of the semantic categories that efficiently spans the semantic content of the plurality of digital images based on said analyzing; or ranking the plurality of sets of semantic categories based on said analyzing. 21. The method of claim 13 , wherein the digital image is comprised in a digital image database, the method further comprising: receiving input specifying one or more keywords for a search query to a digital image database, wherein the digital image database comprises the plurality of digital images, each digital image having a respective semantic category profile; determining a first semantic category profile that corresponds to the one or more keywords by accessing a database of keywords associated with semantic category profiles; determining a respective semantic similarity measure for each digital image in the digital image database based on the first semantic category profile and the respective semantic category profiles of the digital images in the digital image database; and determining one or more digital images in the digital image database based on the values of the semantic similarity measure.