Any interaction at all with anything absorbs the photon and collapses the wave function.
The perhaps best-educated guess as to what is going on: John Archibald Wheeler thinks the real nature of the photon is elusive to our ability to sense it. It's something sort of in-between that we cannot detect directly; we can only detect wave phenomena or particle phenomena so it looks at times like one and at times like the other.
I suppose the Heisenberg uncertainty principle helps a lot with this issue.
On that site there is also a story about Lene Hau:
http://www-groups.dcs.st-and.ac.uk/~history/Mathematicians/Hau.html The incredible part is: "The reason for the behaviour of the Bose-Einstein condensate is essentially due to the Heisenberg Uncertainty Principle for at such low temperatures the momentum of the atoms is known accurately so their positions cannot be accurately known so, in some sense, spread out. Hau produced slow light by inducing quantum interference in the condensate. "