The rise in the intense utilization of images in our daily life resulted in a high volume ofrnimages produced from different sectors of human endeavor. This resulted in the need for anrnefficient management of image data. Recently, Content-based image retrieval has attractedrnmuch attention from the research community. As exact matching is not possible with imagernretrieval, the approach is to use similarity-based matching. Much of the works on similaritybasedrnimage retrieval use the global features (color, shape, texture, etc) of the entire image torncompute similarity score between two images.rnEqually important to using the entire image is the use of salient-objects; objects in an imagernthat are of particular interest to the user, as the basis of similarity-based computation. Therncurrent works on content-based image retrieval do not address very well the issues related tornsalient-objects based image retrieval.rnIn this work, we have proposed an extension to a previous work on image database modelingrnand query processing. To support salient object based image retrieval, we have proposed anrnextension of the data repository model so that spatial features of contained salient objects arerncaptured. Moreover, we proposed an extension to the similarity-based selection operatorrndefined earlier so that salient object based selection operation be part of image databasernsystems for similarity-based image retrieval. We have also proposed spatial operators that canrnbe used to compute spatial relation between an image and contained salient objects. We havernreviewed and presented refined formulations of previous works on spatial relations betweenrnobjects in 2D space to compute spatial relation between salient objects.rnTo demonstrate the viability of salient-objects-based image retrieval, we have extended arnprevious work named EMIMS, to develop a system named EMIMS-S (Extended MedicalrnImage Management System to support Salient objects). We have also used this prototype tornexperimentally show the retrieval effectiveness of salient-objects-based image queries.rnKeywords: Salient-object-based image retrieval, similarity of salient-objects, image database,rnimage data model, similarity-based algebra, spatial relation of salient-objects.