Fast, real-time, estimation of content-sensitive encoding quality for optimized web delivery of images

A request for an image is received. A reduced version of the image is generated. A plurality of reduced distorted images is generated, wherein each reduced distorted image is a reduced version of a different distortion applied to the image. A variation of quality signature of the image is determined, wherein the variation of quality signature of the image comprises a plurality of element signatures, and wherein the plurality of element signatures are determined based on the plurality of reduced distorted images. The image is categorized into one of a plurality of clusters of images, wherein the categorization is based on a similarity between the variation of quality signature of the image and one or more other variation of quality signatures of one or more other images within the plurality of clusters of images. A distorted version of the image based on the categorization is delivered.