  We investigate blending, binarity and photometric biases in crowded-field CCD
imaging. For this, we consider random blend losses, which correspond to the
total number of stars left undetected in unresolved blends. We present a simple
formula to estimate blend losses, which can be converted to apparent magnitude
biases using the luminosity function of the analyzed sample. Because of the
used assumptions, our results give lower limits of the total bias and we show
that in some cases even these limits point toward significant limitations in
measuring apparent brightnesses of ``standard candle'' stars, thus distances to
nearby galaxies. A special application is presented for the OGLE-II BVI maps of
the Large Magellanic Cloud. We find a previously neglected systematic bias up
to 0.2-0.3 mag for faint stars (V~18.0-19.0) in the OGLE-II sample, which
affects LMC distance measurements using RR Lyrae and red clump stars. We also
consider the effects of intrinsic stellar correlations, i.e. binarity, via
calculating two-point correlation functions for stellar fields around seven
recently exploded classical novae. In two cases, for V1494 Aql and V705 Cas,
the reported close optical companions seem to be physically correlated with the
cataclysmic systems. Finally, we find significant blend frequencies up to
50-60% in the samples of wide-field exoplanetary surveys, which suggests that
blending calculations are highly advisable to be included into the regular
reduction procedure.
