Fprintd is a D-Bus daemon that offers libfprint functionality over
the D-Bus interprocess communication bus. By adding this daemon
layer above libfprint, we solve various problems related to multiple
applications simulatenously competing for fingerprint readers.

While it is not very nice to think of a daemon being necessary in
this scenario, fprintd will be launched by D-Bus through the
activation mechanism. This means it is launched only when needed,
and additionally it will shut itself down after a period of inactivity.

(Text copied from link below.)

WWW: http://www.freedesktop.org/wiki/Software/fprint/fprintd/