Gauge constraints and electromagnetic properties of off-shell particles

The consequences of the gauge constraints for off-shellness in the electrom agnetic (EM) vertices have been considered, using Compton scattering as an example. We have found that even if the gauge constraint for the 3-point EM Green function allows for off-shell effects in the charge (Dirac) form fac tor, they vanish in the total Compton scattering amplitude due to the gauge constraint for the 4-point EM Green function only. In addition, the repres entations of the Compton amplitude in terms of either reducible or irreduci ble vertices are equivalent for conserved currents.