The paper abstract says,Under special optical arrangements, physicists can create an image of an object using light that has never interacted with the object. This "ghost imaging" has been around for more than a decade, but it has yet to find much practical use. That could change now that researchers have generated a ghost image of an opaque object, as described in the April Physical Review A.
.A CCD array is placed facing a chaotic light source and gated by a photon counting detector that simply counts all randomly scattered and reflected photons from an object. A “ghost” image of the object is then observed in the gated CCD. Differing from all published ghost-imaging experiments, this setup captures ghosts from scattered and reflected light of an object, instead of the transmitted ones. This new feature is not only useful for practical applications, but is also important fundamentally. It further explores the nonclassical interference nature of thermal light ghost imaging.
You can see an image here. Does anyone understand this?
By the way, I was directed to this by http://www.geekpress.com.
This seems to be a completely different thing than Stanford's Dual Photography, whose video (bottom) is worth a look if you've never seen it.
-g