  We show that the matrix element of a local quark-gluon operator in the photon
state, $<\gamma(k\lambda)|\hat O| \gamma(k\lambda)>$, can be calculated in
lattice QCD. The result is generalized to other quantities involving space-like
photons, including the transition form factor $\gamma\gamma^*\to \pi^0$ and the
virtual-photon-nucleon Compton amplitude $<\gamma^*N |\gamma^*N>$ which can be
used to define the generalized Drell-Hearn-Gerasimov and Bjorken sum rules.
