  The gamma/hadron separation in the imaging air Cherenkov telescope technique
is based on differences between images of a hadronic shower and a gamma induced
electromagnetic cascade. One may expect for a large telescope that a detection
of hadronic events containing Cherenkov light from one gamma subcascade only is
possible. In fact, simulations show that for the MAGIC telescope their fraction
in the total protonic background is about 1.5% to 5.2% depending on the trigger
threshold. It has been found that such images have small sizes (mainly below
400 photoelectrons) which correspond to the low energy primary gamma's (below
100 GeV). It is shown that parameters describing shapes of images from one
subcascade have similar distributions to primary gamma events, so those
parameters are not efficient in all methods of gamma selection. Similar studies
based on MC simulations are presented also for the images from 2 gamma
subcascades which are products of the same pi^0 decay. The ratio of the number
of the expected background from false gamma and one pi^0 to the number of the
triggered high energy photons from the Crab direction has been estimated for
images with a small alpha parameter to show that the occurrence of this type of
protonic shower is the reason for the difficulties with true gamma selection at
low energies.
