Editing Content-based image retrieval (section)

===Semantic retrieval===
''Semantic'' retrieval starts with a user making a request like "find pictures of Abraham Lincoln". This type of open-ended task is very difficult for computers to perform - Lincoln may not always be facing the camera or in the same [[pose (computer vision)|pose]]. Many CBIR systems therefore generally make use of lower-level features like texture, color, and shape.  These features are either used in combination with interfaces that allow easier input of the criteria or with databases that have already been trained to match features (such as faces, fingerprints, or shape matching).  However, in general, image retrieval requires human feedback in order to identify higher-level concepts.<ref name="Rui" />