  Photon-proton ($\gamma p$) interactions with~$Q^2<10^{-2}$~GeV$^2$ and
deep-inelastic scattering ($\gamma^* p$) interactions with photon virtualities
$Q^2>5$~GeV$^2$ are studied at the high energy electron-proton collider HERA.
The transverse energy flow and relative rates of large rapidity gap events are
compared in the two event samples. The observed similarity between $\gamma p$
and $\gamma^* p$ interactions can be understood in a picture where the photon
develops as a hadronic object. The transverse energy density measured in the
central region of the collision, at $\eta^*=0$ in the $\gamma^* p$ centre of
mass frame, is compared with data from hadron-hadron interactions as function
of the CMS energy of the collision.
