VP trees: A data structure for finding stuff fast

Let's say you have millions of pictures of faces tagged with names. Given a new photo, how do you find the name of person that the photo most resembles?

In the cases I mentioned, each record has hundreds or thousands of elements: the pixels in a photo, or patterns in a sound snippet, or web usage data. These records can be regarded as points in high dimensional space. When you look at a points in space, they tend to form clusters, and you can infer a lot by looking at ones nearby.