  A gauge-invariant formalism is presented for the practical treatment of
photo- and electroproduction of pseudoscalar mesons off nucleons that allows an
explicit incorporation of hadronic final-state interactions. The
semi-phenomenological approach is based on a field theory developed by one of
the authors. It generalizes an earlier approach by allowing for systematic
improvement of approximations in a controlled manner. The practical feasibility
is illustrated by applying the lowest-order result to the photoproduction of
both neutral and charged pions.
