Properties of vacuum evaporated ⁸³Rb/^83mKr sources of low-energy conversion electrons, which are under development for monitoring the energy scale stability of the Karlsruhe Tritium Neutrino experiment KATRIN, were examined by the Timepix pixel detector exhibiting the position resolution of at least 55 μm. No distinct local inhomogeneities in the surface distribution of ⁸³Rb/^83mKr were observed. The source diameter derived from the recorded image agrees within 5 % with that expected from evaporation geometry. More precise determination of the actual source diameter is complicated by Compton scattered electrons caused by ⁸³Rb γ-rays.