The production of prompt isolated photons at hadron colliders provides a stringent test of per- turbative Quantum Chromodynamics and can be used to probe the gluon density function of the proton. Using proton-proton collision data provided by the Large Hadron Collider, the ATLAS collaboration has performed numerous cross-section measurements of prompt photon production, among which are a precise measurement of the production of isolated prompt photons in association with heavy flavor jets, a first measurement of the production cross-section of tri-photon final states at a center of mass energy of 8 TeV, and a photon plus jet cross-section measurement at 13 TeV. The results are compared with state-of-the-art theory predictions, indicating several interesting discrepancies.