  We present a general method for incorporating the electromagnetic interaction
into descriptions of hadronic processes based on four-dimensional scattering
integral equations. The method involves the idea of gauging the scattering
equations themselves, and results in electromagnetic amplitudes where an
external photon is effectively coupled to every part of every strong
interaction diagram in the model. Current conservation is therefore implemented
in the theoretically correct fashion. To illustrate our gauging procedure we
apply it to the three-nucleon problem whose strong interactions are described
by standard three-body integral equations. In this way we obtain the
expressions needed to calculate all possible electromagnetic processes of the
three-nucleon system: the electromagnetic form factors of the three-body bound
state, pd->pd gamma, gamma 3He-> pd, gamma 3He-> ppn, etc. As the photon is
coupled everywhere in the strong interaction model, a unified description of
the NNN-gamma NNN system is obtained. An interesting aspect of our results is
the natural appearance of a subtraction term needed to avoid the overcounting
of diagrams.
