  We discuss the possibility of observing ultra high energy cosmic ray sources
inhigh energy gamma rays. Protons propagating away from their accelerators
produce secondary electrons during interactions with cosmic microwave
background photons. These electrons start an electromagnetic cascade that
results in a broad band gamma ray emission. We show that in a magnetized
Universe ($B \gtrsim 10^{-12}$ G) such emission is likely to be too extended to
be detected above the diffusebackground. A more promising possibility comes
from the detection of synchrotron photons from the extremely energetic
secondary electrons. Although this emission is produced in a rather extended
region of size $\sim 10Mpc$, it is expected to be point-like and detectable at
GeV energies if the intergalactic magnetic field is at the nanogauss level.
