[GhostVII]

Couldn't you just take whatever image you want to convert to a RAW file, make a really large high quality print out of it, and then take a picture of that? I would imagine that with the right lighting setup (and a really high quality printout) it would be pretty hard to tell that it is a picture of a picture.

[kortex]

Nope. Light is a 5D wavefront. Each x,y,z of origin in the real world is actually a sum of photons from many directions, scattering to many other directions. So you have two angular components. At times, phase matters too, and frequency, so each photon needs perhaps 7 parameters to capture its state, (x,y,z,θ,φ,ψ,λ).

On top of that, you have diffraction effects in the optics, chromtic aberration, and even some birefringence effects.

Algorithms exist which can detect if an image has been cropped, and what region of the original it came from. I'll leave as an exercise to the reader how that works :) hint: keyword is "media forensics"