  The algorithms used by the ATLAS Collaboration to reconstruct and identify
prompt photons are described. Measurements of the photon identification
efficiencies are reported, using 4.9 fb$^{-1}$ of pp collision data collected
at the LHC at $\sqrt{s}$=7 TeV and 20.3 fb$^{-1}$ at $\sqrt{s}$=8 TeV. The
efficiencies are measured separately for converted and unconverted photons, in
four different pseudorapidity regions, for transverse momenta between 10 GeV
and 1.5 TeV. The results from the combination of three data-driven techniques
are compared to the predictions from a simulation of the detector response,
after correcting the electromagnetic shower momenta in the simulation for the
average differences observed with respect to data. Data-to-simulation
efficiency ratios used as correction factors in physics measurements are
determined to account for the small residual efficiency differences. These
factors are measured with uncertainties between 0.5% and 10% in 7 TeV data and
between 0.5% and 5.6% in 8 TeV data, depending on the photon transverse
momentum and pseudorapidity.

High Energy Physics - Experiment