Objects were automatically detected using the task DAOPHOT/DAOFIND. This task
performs a convolution with a gaussian having characteristics previously
chosen taking into account the seeing in each frame (FWHM of the star-like
profiles in the image) as well as the CCD readout noise and
gain. Then, objects are identified as the peaks of the convolved image that
are higher than a given threshold
above the local sky background (chosen as approximately equal to 5 
of the image mean sky flux).
A list of detected objects is thus produced and interactively corrected on
the displayed image so as to discard spurious objects, add undetected ones
and dispose of false detections caused by the events flagged in the previous
section (all of which concerning only a few percent of objects). Notice that
all objects that were ``hand-added'' to the final list are both very faint
and very low surface brightness ones, though still visible by eye inspection.
The completeness of the catalogue is by no means dependent on this correction.