Pam_fprint is a pam module which uses libfprint's fingerprint verification functionality to implement a fingerprint-based authentication scheme.
this means that you may be able to authenticate against every service, tool, application or whatever that uses pam as an authentication mechanism; for example ssh, gdm/kdm/xdm, most screen savers, login, su, sudo, etc.
previously, linux support for such devices has been scattered amongst different projects (many incomplete) and inconsistent in that application developers would have to implement support for each type of fingerprint reader separately. the idea is to change that by providing a central system to support all the fingerprint readers as it's possible to get hands on.
libfprint is the centre of efforts, this component does the dirty job of talking to fingerprint reading devices, and processing fingerprint data.
this library depends on the new libusb, which performs asynchronous callbacks, allowing fprint to perform non-blocking device tasks. old synchronous library has been deprecated in favor of the new libusb-1.0.