  We present a novel method, based on vortex imaging by low-temperature
scanning electron microscopy (LTSEM), to directly image the sheet-current
distribution in YBa2Cu3O7 dc SQUID washers. We show that the LTSEM vortex
signals are simply related to the scalar stream function describing the
vortex-free circulating sheet-current distribution J. Unlike previous inversion
methods that infer the current distribution from the measured magnetic field,
our method uses pinned vortices as local detectors for J. Our experimental
results are in very good agreement with numerical calculations of J.
