  We present a comparison between the spectroscopic catalog of the HDF recently
published by Cohen et al and the redshifts measured by our group for those
objects using photometric techniques. We perform this comparison in order to
characterize the errors associated to the photometric redshift technique. The
spectroscopic sample includes over 140 objects in the HDF proper, representing
the deepest, cleanest, most complete spectroscopic catalog ever compiled. We
study each object for which our redshift and the one measured by Cohen et al
disagree. In most cases the photometric evidence is strong enough to call for a
careful review of the spectroscopic values, as they seem to be in error. It is
possible to characterize the systematic errors associated to our technique,
which when combined with the photometric errors allow us to obtain complete
information on the redshift of each galaxy and its associated confidence
interval, regardless of apparent magnitude. One of the main conclusions of this
study is that, to date, all the redshifts from our published catalog that have
been checked have been shown to be correct (within the stated confidence
limits). This implies that our galaxy template set is a fair representation of
the galaxy population at all redshifts (0<z<6) and magnitudes (R<24) explored
to date. On the other hand, spectroscopy of faint sources is subject to unknown
and uncharacterized systematic errors, that will in turn be transmitted to any
photometric redshift technique which uses spectroscopic samples as calibration.
Our analysis proves that photometric redshift techniques can and must be used
to extend the range of applicability of the spectroscopic redshift
measurements. (Abridged)
