New Scientist: A normal digital camera can take snaps of objects not directly visible to its lens, US researchers have shown. The "ghost imaging" technique could help satellites take snapshots through clouds or smoke.

Physicists have known for more than a decade that ghost imaging is possible. But, until now, experiments had only imaged the holes in stencil-like masks, which limited its potential applications.

Now Yanhua Shih of the University of Maryland, Baltimore, and colleagues at the US Army Research Laboratory, also in Maryland, have now taken the first ghost images of an opaque object - a toy soldier.

Not everyone agrees that quantum effects are at work in ghost imaging, though. Baris Erkmen and Jeffrey Shapiro of the Massachusetts Institute of Technology, Cambridge, US, point out in a recent paper that classical physics says light sources produce numbers of uncoordinated photons, not correlated quantum pairs.

They suspect ghost images might be produced without a quantum link between photon pairs, purely because some photons are just similar.

Related Link
Physical Review A (DOI: 10.1103/PhysRevA.77.041801)