We analyze the state of the art of content-based retrieval in Earth
observation image archives focusing on complete systems showing promise for
operational implementation. The different paradigms at the basis of the main
system families are introduced. The approaches taken are analyzed, focusing in
particular on the phases after primitive feature extraction. The solutions
envisaged for the issues related to feature simplification and synthesis,
indexing, semantic labeling are reviewed. The methodologies for query
specification and execution are analyzed