Positrons don't merely look like time-reversed electrons, and it's not limited to Feynman diagrams. Everything we know about those particles, experimentally and

Positrons don't merely look like time-reversed electrons, and it's not limited to Feynman diagrams. Everything we know about those particles, experimentally and in our best theory, says that they literally are identical but for a minus sign on the time variable. And it does work for photons because there is an anti-photon: the photon itself. The particle is symmetric under time reversal.