most proposed content based database systems aim to retrieve a small set of candidate images which include the desired image. the successful retrieval of the best candidate then relies on the final user judgement. in, the authors have used polygonal approximation, while a set of features like boundary/perimeter, elongation (major axis / minor axis), number of holes, etc, have been used a combination of heuristic shape features such as area, circularity, eccentricity, major axis orientation and a set of algebraic moment invariants. they have also used other features such as color, texture, and even sketch features.