I should have mentioned this was done client-side, by a Python script:

http://code.google.com/p/fftresize/source/browse/fftresize.p...

Like so (edit: note that you'll have to edit the image first to make it grayscale, and even then this uses a lot of memory...):

    $ python fftresize.py suspect-number-2.JPG 2.0

I just uploaded the image to S3 to share. The script isn't great (grayscale only) because it was written for a blog post to demonstrate the interpolation method, but I might as well work on it this weekend.