  A model of $\pi N$ pair photoproduction on nuclei at high momentum transfer
is presented. The $A(\gamma,\pi N)B$ reaction amplitude is obtained by means of
an extended impulse approximation, according to which the nuclear wavefunction
includes delta-isobar components in addition to nucleon components. A
one-particle transition operator is defined in terms of the two-body $\gamma
N\to\pi N$ and $\gamma \Delta\to\pi N$ photoproduction amplitudes. Direct and
exchange mechanisms of the nuclear photoproduction reaction are studied, and
numerical estimates are made and presented of $^{12}{\rm C}(\gamma,\pi^-
p){^{11}{\rm C}}$ and $^{12}{\rm C}(\gamma,\pi^+ p){^{11}{\rm Be}}$
differential cross sections at photon incident energies in the $\Delta(1232)$
resonance region.
