The goal of query optimization is to select an efficient query evaluation strategy. Queryrnoptimization is a widely studied problem in the context of traditional database systems. Asrna result many query optimization techniques have been developed and integrated into thernquery processing module of these database systems. Due to the differences in queryrnprocessing strategy followed by content-based image database systems, query optimizationrnin these systems is different.rnIn recent years, the number of image used in different application areas is increasing at arnhigh rate. As a result, many content-based image retrieval systems and content-basedrnimage database systems have been developed. These systems have become important tornmanage image queries based on low level features when the size of images to be managedrnis small. However, as the size of image collection to be managed increases, these systemsrncould not be efficient. This is because the underlying database do not provide queryrnoptimization scheme for similarity-based image queries.rnIn this thesis we developed heuristic-based query optimization techniques that transformrndeclarative query posed on content-based image database into more efficient form. To testrnthe performance of the proposed optimization techniques we conducted experiments. Thernresult of our experimental tests showed that our optimization techniques have brought arnsignificant cost saving by reducing execution time of queries.rnIn addition to the query optimization techniques, we proposed a method of integratingrnthese query optimization techniques with existing content-based image database systems.rnAs the query optimizer of commercial database systems that support content-based imagernprocessing are not fully extensible, we proposed to develop and integrate a query optimizerrninto the Image query processing module previously proposed. This requires therndevelopment of query optimizer that implements the optimization techniques. Hence, wernhave identified the requirement of query optimizer for content-based image database andrnpresented the design of an extensible rule-based query optimizer.rnKeywords: Query optimization, image database, similarity-based query processing,rnOptimization for content-based image database.