The configuration files for Debian release of sane are in /etc/sane.d.
Each scanner backend has a configuration file which lists device names
which correspond to that scanner.  By default, each configuration file
contains the device /dev/scanner.  Either create a symbolic link from
/dev/scanner to the appropriate device, or place any device names in
the configuration files.  See find-scanner below to determine which
generic SCSI device your scanner is connected to.

If your scanner does not work, edit the file /etc/sane.d/dll.conf.
Verify that your scanner is not commented out.  You may need to
comment out all other scanners in dll.conf.  It shouldn't matter, but
sometimes it does.

For information on configuring and trouble-shooting the various SANE
components, please refer to the manual pages listed below:

       Regarding:  Read:
       -----------------  ------------------------------------------
       scanimage  scanimage(1)
       xscanimage  xscanimage(1)
       saned  saned(1)
       xcam  no man-page---see xcam.README

       Dynamic loading  sane-dll(5)
       Mustek scanners  sane-mustek(5) and sane-scsi(5)
       UMAX scanners  sane-umax(5) and sane-scsi(5)
       HP scanners  sane-hp(5) and sane-scsi(5)
       Networking  sane-net(5) and saned(1)
       PINT scanners  sane-pint(5)
       QuickCam  sane-qcam(5)

Please note that the default configuration uses sane-dll as the
top-level backend.  Hence it is probably a good idea to start with
reading sane-dll(5).  The top-level backend is determined by the
libsane.* symlinks in /usr/local/lib/.

If you encounter any problems with getting your device(s) recognized,
try setting the various environment variables that are there to assist
in debugging such problems.  The environment variables are documented
in the relevant manual pages.  For example, to get the maximum amount
of debug information when testing a Mustek scanner, set environment
variables SANE_DEBUG_DLL, SANE_DEBUG_MUSTEK, and SANE_DEBUG_SANEI_SCSI
to 128 and then invoke scanimage or whatever program you're trying to
debug.  For a Mustek scanner at /dev/scanner, you might want to invoke
scanimage as follows:

scanimage -d mustek:/dev/scanner -h

If this works, you could try to acquire an image with:

scanimage -d mustek:/dev/scanner >t.pnm

If you are not sure what generic SCSI device your scanner is connected
to, try the command tools/find-scanner.  It is normally sufficient to
invoke the program without any arguments.  Invoking this command
should produce output similar to this:

  $ tools/find-scanner
  find-scanner: found "MUSTEK MFC-06000CZ 1.01" at device /dev/scanner
  find-scanner: found "MUSTEK MFC-06000CZ 1.01" at device /dev/sge


HP scanners are sometimes problematic with sane.  See
<http://www.kirchgessner.net/sanehpfaq.html> for more information on
HP scanners.