Seriously geeky: searching in metric spaces

It's easy to see how to organise a database if you want to be able to, say, find all the people in it whose names are between "Charybdis" and "Scylla" in alphabetical order. But how would you organise it if you want to find all the people whose pictures look most like a particular sample picture, when all you have is a tool that measures how similar two pictures are? There's a family of very general approaches to the problem called "metric space searches"; in this approach, we don't need to know anything about what we're storing except that we can measure the distance between two items and get a sensible answer.

I thought I'd invented a smashing new algorithm for searching in metric spaces. But I'm having a hard time finding out if it's any good.

( Techical content follows )

Going to a different party tonight...

For those who don't know, I'm unlikely to be at the God party tonight, because I'm going to my Mum's 60th birthday party! Sorry to miss you all. If that party finishes before very late, I might try and make a late night appearance, but don't count on it.

Just went downstairs and saw spikeylady and lilithmagna asleep together, her head on his manly chest, both sleepily smiling... FRUBBLE!