"Seam carving for content-aware image resizing"
And what's awesome is while it's a brilliant idea... it's also relatively simple to implement, or at least straight-forward... there's probably an infinite amount of "art" to it as well, but...
If you have ANY interest in photography, you really have to watch this:
Thanks to indomitability for pointing this out to me. :)
And... here's a prototype: Liquid Resize
And an online demo: Seam Carving Demo
And some GPL'd source: Smart Image Resizing
And the original PDF is available from: Selected Publications, Ariel Shamir