Sensitivity of the Auger Observatory to ultra high energy photon composition through inclined showers

We report a calculation of the expected rate of inclined air showers induced by ultra high energy cosmic rays to be obtained by the Auger Southern Observatory assuming different mass compositions. We describe some features that can be used to distinguish photons at energies as high as 10${}^{20}$ eV. The discrimination of photons at such energies will help to test some models of the origin of ultra-high-energy cosmic rays.