Today I created a presentation on Caliph and Emir and I looked up how long these open source projects are now part of my (online & research) life. In July 2004 I put the first open source version of Caliph & Emir online and ~ 6.700 downloads happened from then till now. Furthermore the Java Web Start files of Caliph and Emir were accessed about 1.300 times. Lire was more successful: Going online in 2006 it was ~3.600 times download till now.
Taking a look around I have to say that Caliph is still the only MPEG-7 tool for semantic descriptions. Due to the fact that it is a prototype (with virtually no productive use) i assume that there is currently no need for such a tool. Reported use is focused on MPEG-7 development and research projects. Lire on the other hand has a more active user base: I know several projects where Lire is used. Seems like there actually is a need for an open source Java library for content based image retrieval.