For the analysis of data taken by Imaging Air Cherenkov
Telescopes (IACTs), a large number of air shower simulations are
needed to derive the instrument response. The simulations are very
complex, involving computational and memory-intensive calculations,
and are usually performed repeatedly for different observation
intervals to take into account the varying optical sensitivity of
the instrument. The use of generative models based on deep neural
networks offers the prospect for memory-efficient storing of huge
simulation libraries and cost-effective generation of a large number
of simulations in an extremely short time. In this work, we use
Wasserstein Generative Adversarial Networks to generate photon
showers for an IACT equipped with the FlashCam design, which has
more than 1,500 pixels. Using simulations of the
H.E.S.S. experiment, we demonstrate the successful generation of
high-quality IACT images. The analysis includes a comprehensive
study of the generated image quality based on low-level observables
and the well-known Hillas parameters that describe the shower shape.
We demonstrate for the first time that the generated images have
high fidelity with respect to low-level observables, the Hillas
parameters, their physical properties, as well as their
correlations. The found increase in generation speed in the order
of 105 yields promising prospects for fast and memory-efficient
simulations of air showers for IACTs.