The backend sane-bh has been added to the SANE CVS library. I'm hoping to get the frontend scanadf into the CVS library as well. Until that time these 1.0.3 based patches will be the best way to get scanadf.
The backend sane-bh and the frontend scanadf are packaged together as a patch to the latest SANE distribution. Hopefully, each will become part of the SANE distribution. Until then, the latest versions will be made available here as a patch to the latest SANE distribution.
The patch is based on the latest SANE distribution (sane-1.0.3.tar.gz) which can be obtained from the SANE Download Page
patch -p 1 < sane-1.0.3-bh-0.3.patch
./configure make make install (as root)