Image descriptor identifiers are used for content-based search. A plurality of descriptors is determined for an image. The descriptors represent the content of the image at respective interest points identified in the image. The descriptors are mapped to respective descriptor identifiers. The image can thus be represented as a set of descriptor identifiers. A search is performed on an index using the descriptor identifiers as search elements. A method for efficiently searching the inverted index is also provided. Candidate images that include at least a predetermined number of descriptor identifiers that match those of the image are identified. The candidate images are ranked and at least a portion thereof are presented as content-based search results.