Get somewhere (don't remember) AGFA Scanwise, containing the firmware. Then modify /etc/sane.d/snapscan.conf:
That's it.

I have been using an HP ScanJet 4100C with my linux computer for a number of years. I primarily use it to scan old pictures into GIMP for restoration or enhancement. Even though I always kept the outside of the glass clean, I have noticed in the last year that the inside of the glass was developing a cloudy residue. I finally decided to do something about it. Before getting started, I locked the scan head using the sliding green button on the bottom of the scanner. If you open the cover, there...

Distribution: Slackware 13.1 (Update) These procedures relate to Slackware 14.0 64bit as well.
Distribution Edition: 32bit
Driver: mfcj220lpr-1.1.1-1.i386.rpm
Driver: mfcj220cupswrapper-1.1.1-3.i386.rpm
Driver: brscan3-0.2.11-4.i386.rpm
Driver: brscan-skey-0.2.1-3.i386.rpm
SANE version: Sane-1.0.21
CUPS version: cups-1.4.5
***Note***For 64bit Slackware you will need to install at least the glibc-solibs-2.15_multilib-x86_64-7alien.txz and cups-compat32-1.5.4-x86_64-2compat32.txz...