The three beam lines of the DESY II Test Beam Facility provide electrons with a selectable momentum of 1-6 GeV/c and are widely used in the R&D community of HEP. A feasability study for a photon tagged beam line was performed this year. Here, secondary bremsstrahlung photons are generated in the test beam area and electrons are a deflected by the Big Red Magnet of beam line TB21. With such a setup the electron/gamma separation capability of calorimeter can be tested. In addition it provides an indirect energy measurement of the bremsstrahlung photons. Simulations and measurement results are presented.