1. A method of increasing information content for content-based image retrieval (CBIR) systems, comprising the steps of: providing a CBIR database, said database comprising an index for a plurality of stored digital images using a plurality of feature vectors, said feature vectors corresponding to distinct descriptive characteristics of said images; calculating a visual similarity parameter value based on a degree of visual similarity between features vectors of an incoming image being considered for entry into said database and feature vectors associated with a most similar of said stored images, and determining whether to store or how long to store said feature vectors associated with said incoming image in said database based on said visual similarity parameter value.