Ask HN: How to find the right developer for the job?

Hey, I am a graphic designer and front end developer. I've tossed around some php and rails - enough to know that I should let other people do that. I often find myself in the unenviable position of having to hire programmers for contract based projects, and it feels like a shot in the dark as to whether or not I find a good one for the job when the time comes.

At the moment I am looking for a collaborator on a project that I am working on. The first stage is to design and develop a system for uploading photos of garments against a white wall that can remove the background from the image. We're trying to avoid flash, so I'm looking for someone who can chop out some crazy amazing java / javascript solution and integrate it into a php based cms. (Probably SilverStripe.)

I've been posting on twitter, but I haven't had a ton of luck luring in anything but agencies and outsourcers. And I've had bad luck in the past with formal job posts.

Anyone have any advice? I hate the idea of crowdsourcing sites like elance...