A nice and thorough book about raytracing-like techniques (including photon tracing), and their capabilities is "Advanced Global Illumination" (http://sites.edm

A nice and thorough book about raytracing-like techniques (including photon tracing), and their capabilities is "Advanced Global Illumination" (http://sites.edm.uhasselt.be/agibook http://sites.edm.uhasselt.be/agibook). It is very interesting.