This paper presents a comparative study of color descriptors for content-based image retrieval on the Web. Several image descriptors were compared theoretically and the most relevant ones were implemented and tested in two different databases. The main goal was to find out the best descriptors for Web image retrieval. Descriptors are compared according to the extraction and distance functions complexities, the compactness of feature vectors, and the ability to retrieve relevant images. © 2008 IEEE. 163170A. E. Abdel-Hakim and A. A. Farag. 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