1. A method for efficiently and accurately detecting changes in feature data, comprising: determining, by at least one electronic circuit, first vectors for first features extracted from a first image; comparing, by the electronic circuit, the first vectors with pre-defined second vectors; classifying, by the electronic circuit, the first features into a plurality of classes based on the results of the comparing step; and analyzing the first image to determine if any one of the first features of at least one of the plurality of classes indicates that a relevant change has occurred in relation to an object represented thereby.