We report the results of STM-induced photon emission experiments performed on several types of nanostructures deposited or fabricated onto atomically flat (111) gold surfaces. We demonstrate the simultaneous observation of contrasts both from chemically inhomogeneous and homogeneous nanostructures. In the latter case the mechanisms of the contrast involves only geometrical factors and we observe a resonance in excitation spectroscopy that we attribute to a localized plasmon oscillation mode. Our results illustrate the opportunities offered by STM-induced photon emission experiments as a photophysical probe technique with high-spatial resolution.