  The Large High Altitude Air Shower Observatory~(LHAASO) is one of the most
sensitive gamma-ray detector arrays currently operating at TeV and PeV
energies. Recently the LHAASO experiment detected ultra-high-energy~(UHE;
$E_{\gamma}\gtrsim 100~\mathrm{TeV}$) photon emissions up to $1.4~\mathrm{PeV}$
from twelve astrophysical gamma-ray sources. We point out that the detection of
cosmic photons at such energies can constrain the photon self-decay motivated
by superluminal Lorentz symmetry violation~(LV) to a higher level, thus can put
strong constraints to certain LV frameworks. Meanwhile, we suggest that the
current observation of the PeV-scale photon with LHAASO may provide hints to
permit a subluminal type of Lorentz violation in the proximity of the Planckian
regime, and may be compatible with the light speed variation at the scale of
$3.6\times 10^{17}~\mathrm{GeV}$ recently suggested from gamma-ray burst~(GRB)
time delays. We further propose detecting PeV photons coming from extragalactic
sources with future experiments, based on LV-induced threshold anomalies of
$e^{+}e^{-}$ pair-production, as a crucial test of subluminal Lorentz
violation. We comment that these observations are consistent with a
D-brane/string-inspired quantum-gravity framework, the space-time foam model.
