  We present a reanalysis of single photon production from relativistic
collision of lead nuclei at CERN SPS measured by the WA98 experiment. The
refinements include use of iso-spin and shadowing corrected NLO pQCD treatment
for prompt photon production using an optimized scale for factorization,
renormalization, and fragmentation and use of hydrodynamics suited for
non-central collisions along with a well tested equation of state admitting a
quark-hadron phase transition. A quantitative explanation of the data requires
a large initial temperature (at a small formation time of about 0.2 fm/$c$) and
a moderate increase in the prompt yield which could perhaps be attributed to
the Cronin effect in nuclei. The data can also be explained using a moderate
initial temperature (at a formation time of about 1 fm/$c$) with a very large
$K$-factor multiplying the prompt yield. We show that different initial times
give rise to different values for the elliptic flow parameter $v_2$ for thermal
photons. We also show that a measurement of $v_2$ for thermal photons could
also distinguish between the scenarios with or without a phase transition.
