Is there software that would allow me to tag faces in a library of over 1 million photos?

I have used Picasa for smaller numbers of photos, and I like how it groups faces together, so that you can tag all instances of a face in one go.

My objective is, once all the tagging is done, to be able to quickly find all photos of a person. Essentially the face tagging feature in Picasa, but scaling to thousands of faces and over 1 million photos.

It can work on any version of Windows or Linux. I would need something very inexpensive to try it out, but if it works well then I may have a budget of a few hundred dollars.