  Production of lepton pairs in gamma p -> e-e+ p reaction is studied at photon
energies up to 1 GeV. We show that even if lepton charge is not measured there
are extensive kinematical regimes where the nuclear process dominates over the
Bethe-Heitler contribution. The decomposition is performed of the unpolarized
cross section for the virtual Compton scattering in terms of response
functions. These are expressed in terms of a polarization density matrix of the
virtual photon and are shown to be sensitive to the properties of baryon
resonances in the first and the second resonance regions. In the analysis a
unitary K-matrix model is used, based on an effective Lagrangian including
nucleon, mesons, and baryon resonances with masses up to 1.7 GeV. Results of
the model are compared with data for real-photon Compton scattering and
predictions are given for observables in photoproduction of lepton pairs.
