  We report results of a new analysis of a deep 95 mu imaging survey with the
photo-polarimeter ISOPHOT on board the Infrared Space Observatory, over a half
square degree area within the Lockman Hole. To this end we exploit a newly
developed parametric algorithm able to identify and clean spurious signals
induced by cosmic-rays impacts and by transient effects and non-linearities in
the detectors. These results provide us with the currently deepest -- to our
knowledge -- far-IR image of the extragalactic sky. Within the survey area we
detect thirty-six sources with S/N>3 (corresponding to a flux of 16 mJy),
making up a complete flux-limited sample around 100$ mJy. Reliable sources are
detected, with decreasing but well-controlled completeness, down to 20 mJy. The
source extraction process and the completeness, the photometric and astrometric
accuracies of this catalogue have been tested by us with extensive simulations
accounting for all the details of the procedure. We estimate source counts down
to a flux of ~30 mJy, at which limit we evaluate that from 10% to 20% of the
cosmic IR background has been resolved into sources. The 95mu galaxy counts
reveal a steep slope at fluxes lower than 100 mJy (alpha~1.6), in excess of
that expected for a non-evolving source population. The shape of these counts
agrees with those determined by ISO at 15 and 175 mu, and starts setting strong
constraints on the evolution models for the far-IR galaxy populations.
