We reached a milestone here! Sebastian Kielmann reported that he used LIRe to index a million images. While that’s actually no problem he further managed to search through the images in < 1 second! Whoot!
Sebastian used the metric index, which implements the ideas of Giuseppe Amato. The approach is easy, but works out really fine. Currently CEDD is the standard descriptor, but others are integrated easily. However, using the metric index is not trivial and requires some knowledge on the process. Also the results are approximate and might differ from the results obtained by linear search.