  We present the microlensing optical depth towards the Galactic bulge based on
the detection of 99 events found in our Difference Image Analysis (DIA) survey.
This analysis encompasses three years of data, covering ~ 17 million stars in ~
4 deg^2, to a source star baseline magnitude limit of V = 23. The DIA technique
improves the quality of photometry in crowded fields, and allows us to detect
more microlensing events with faint source stars. We find this method increases
the number of detection events by 85% compared with the standard analysis
technique. DIA light curves of the events are presented and the microlensing
fit parameters are given. The total microlensing optical depth is estimated to
be tau_(total)= 2.43^(+0.39/-0.38) x 10^(-6) averaged over 8 fields centered at
l=2.68 and b=-3.35. For the bulge component we find
tau_(bulge)=3.23^(+0.52/-0.50) x 10^(-6) assuming a 25% stellar contribution
from disk sources. These optical depths are in good agreement with the past
determinations of the MACHO Alcock et al. (1997) and OGLE Udalski et al. (1994)
groups, and are higher than predicted by contemporary Galactic models. We show
that our observed event timescale distribution is consistent with the
distribution expected from normal mass stars, if we adopt the stellar mass
function of Scalo (1986) as our lens mass function. However, we note that as
there is still disagreement about the exact form of the stellar mass function,
there is uncertainty in this conclusion. Based on our event timescale
distribution we find no evidence for the existence of a large population of
brown dwarfs in the direction of the Galactic bulge.
