  We study the thermal emission of photons from hot and dense strongly
interacting hadronic matter at temperatures close to the expected phase
transition to the Quark-Gluon Plasma (QGP). Earlier calculations of photon
radiation from ensembles of interacting mesons are re-examined with additional
constraints, including new production channels as well as an assessment of
hadronic form factor effects. Whereas strangeness-induced photon yields turn
out to be moderate, the hitherto not considered t-channel exchange of omega
mesons is found to contribute appreciably for photon energies above ~1.5 GeV.
The role of baryonic effects is assessed using existing many-body calculations
of lepton pair production. We argue that our combined results constitute a
rather realistic emission rate, appropriate for applications in relativistic
heavy-ion collisions. Supplemented with recent evaluations of QGP emission, and
an estimate for primordial (hard) production, we compute photon spectra at SPS,
RHIC and LHC energies.
