  Lorentz invariance violation (LIV) introduced as a generic modification to
particle dispersion relations can change the photon energy threshold of
pair-production, which modifies the expected gamma-ray flux from astrophysical
sources. In this work, we review this phenomenon and explore its consequences
through the derived effects in the optical depth. Then, by looking for
subluminal LIV signatures in TeV gamma-ray spectra, we present stringent limits
to the LIV energy scale at leading order n=1 and 2. And finally, we present the
predicted flux of GZK-photons including LIV, in the astrophysical scenario
which best describes UHECR data.
