  In this paper we evaluate sources of background for the $\gamma p \to \omega
p$, with the $\omega$ detected through its $\pi^0 \gamma$ decay channel, to
compare with the experiment carried out at ELSA. We find background from
$\gamma p \to \pi^0 \pi^0 p$ followed by decay of a $\pi^0$ into two $\gamma$,
recombining one $\pi^0$ and one $\gamma$, and from the $\gamma p \to \pi^0 \eta
p$ reaction with subsequent decay of the $\eta$ into two photons. This
background accounts for the data at $\pi^0 \gamma$ invariant masses beyond 700
MeV, but strength is missing at lower invariant masses which was attributed to
photon misidentification events, which we simulate to get a good reproduction
of the experimental background. Once this is done, we perform an event mixing
simulation to reproduce the calculated background and we find that the method
provides a good description of the background at low $\pi^0 \gamma$ invariant
masses but fakes the background at high invariant masses, making background
events at low invariant masses, which are due to $\gamma$ misidentification
events, responsible for the background at high invariant masses which is due to
the $\gamma p \to \pi^0 \pi^0 p$ and $\gamma p \to \pi^0 \eta p$ reactions.
