Background rejection algorithms for Pi of the Sky

Pi of the Sky is a system of wide field-of-view robotic telescopes,
which search for short timescale astrophysical phenomena, especially
for prompt optical GRB emission. The system was designed for autonomous
operation, monitoring a large fraction of the sky with 12m-13m range and
time resolution of the order of 1 - 10 seconds. In October 2010 the first unit of the
final Pi of the Sky detector system, with 4 CCD cameras, was successfully installed
in the INTA El Arenosillo Test Centre in Spain. We use data collected by this detector to
develope new, improved algroithms for rejecting backgrounds to GRB identification.
Considered backgrouds include: clouds, star saturation effects, mount movements,
hotpixels, opened shutter effects.