Re: What specific process gives rise to blackbody photons?

The formation of a blackbody spectrum isn't a process like free-free
emission (bremsstrahlung) or spontaneous emission. The photons don't come
directly from the movement of an electron. Instead, the source of photons
depends entirely on what object is giving rise to the blackbody spectrum. 

If the object in question is a star, then the photons come from nuclear
fusion. If it's the canonical blackbody they always talk about in physics
books (a heated cavity with a rough inner surface and one small hole to let
light out) then the photons come from the thermally excited walls of the
chamber. What actually forms the blackbody spectrum is the fact that the
photons bounce around zillions of times before escaping. Each time the
photon bounces it's re-emitted with a different amount of energy. The
result of all this bouncing is the statistical distribution that bears
Bolztmann's name. 

So it doesn't matter where the photons come from. As long as the object
that's producing them is optically thick (meaning it allows for a large
number of collisions before the photon is released) and in thermal
equilibrium then the energy distribution of the resultant light will be a
blackbody curve. 

Reference: Rybicki, G.B., and Lightman, A.P. "Radiative Processes In
Astrophysics"  Wiley Interscience, 1979.