  We investigate the measurement of Hanbury Brown-Twiss (HBT) photon
correlations as an experimental tool to discriminate different sources of
photon enhancement, which are proposed to simultaneously reproduce the direct
photon yield and the azimuthal anisotropy measured in nuclear collisions at
RHIC and the LHC. To showcase this, we consider two different scenarios in
which we enhance the yields from standard hydrodynamical simulations. In the
first, additional photons are produced from the early pre-equilibrium stage
computed from the \textit{bottom-up} thermalization scenario. In the second,
the thermal rates are enhanced close to the pseudo-critical temperature
$T_c\approx 155\,\text{MeV}$ using a phenomenological ansatz. We compute the
correlators for relative momenta $q_o, \,q_s$ and $q_l$ for different
transverse pair momenta, $K_\perp$, and find that the longitudinal correlation
is the most sensitive to different photon sources. Our results also demonstrate
that including anisotropic pre-equilibrium rates enhances non-Gaussianities in
the correlators, which can be quantified using the kurtosis of the correlators.
Finally, we study the feasibility of measuring a direct photon HBT signal in
the upcoming high-luminosity LHC runs. Considering only statistical
uncertainties, we find that with the projected $\sim 10^{10}$ heavy ion events
a measurement of the HBT correlations for $K_\perp<1\, \text{GeV}$ is
statistically significant.
