  Thermal photons produced in heavy-ion collision experiments are an important
observable for understanding quark-gluon plasma (QGP). The thermal photon rate
from the QGP at a given temperature can be calculated from the spectral
function of the vector current correlator. Extraction of the spectral function
from the lattice correlator is known to be an ill-conditioned problem, as there
is no unique solution for a spectral function for a given lattice correlator
with statistical errors. The vector current correlator, on the other hand,
receives a large ultraviolet contribution from the vacuum, which makes the
extraction of the thermal photon rate difficult from this channel. We therefore
consider the difference between the transverse and longitudinal part of the
spectral function, only capturing the thermal contribution to the current
correlator, simplifying the reconstruction significantly. The lattice
correlator is calculated for light quarks in quenched QCD at $T=470~$MeV ($\sim
1.5\, T_c$), as well as in 2+1 flavor QCD at $T=220~$MeV ($\sim 1.2 \, T_{pc}$)
with $m_{\pi}=320$ MeV. In order to quantify the non-perturbative effects, the
lattice correlator is compared with the corresponding
$\text{NLO}+\text{LPM}^{\text{LO}}$ estimate of correlator. The reconstruction
of the spectral function is performed in several different frameworks, ranging
from physics-informed models of the spectral function to more general models in
the Backus-Gilbert method and Gaussian Process regression. We find that the
resulting photon rates agree within errors.
