I stumbled across a way to make the Pi work as a scanner server. This worked with a Brother all-in-one device that does not have any drivers available for the Pi. It seems like it would work for any make and model of scanner that uses sane
. It was much easier than setting up the Pi to serve an HP scanner using hpaio. The method is detailed by Piotr Król at http://blog.3mdeb.com/2015/10/27/linux/
. The Pi knows almost nothing about the scanner, it just serves a USB connection to the client computer with a program called usbip
(available in the Raspbian Jessie repository). The client provides all the drivers and other software to run the scanner.