My Brother DCP-7020 printer/scanner combo device is several years old, and, while supported on Linux, the drivers provided by Brother are 5+ years old, so while they install fine it always requires some manual fiddling to make the scanner part work.
After getting the udev rules installed (manually or via provided .deb package), the driver libraries appeared to be in the wrong directory, they lived in /usr/lib64 instead of /usr/lib/x86_64-linux-gnu
# for f in /usr/lib64/* ; do [ -d $f ] || sudo ln -s $f /usr/lib/x86_64-linux-gnu/$(basename $f) ; done ; for f in /usr/lib64/sane/* ; do sudo ln -s $f /usr/lib/x86_64-linux-gnu/sane/$(basename $f) ; done
# sudo scanimage -L
device `brother2:bus3;dev1' is a Brother DCP-7020 USB scanner
Well, actually, while it detected the scanner and allowed xsane and simple-scan to run, both programs reported errors when trying to initiate a scan.
(I will update if/when I figure out how to make this work)