[en] Photon-proton (γp) interactions with Q² < 10^-2 GeV² and deep-inelastic scattering (γ^*p) interactions with photon virtualities Q² > 5 GeV² 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 γp and γ^*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 η^* = 0 in the γ^*p centre of mass frame, is compared with data from hadron-hadron interactions as function of the CMS energy of the collision. (orig.)