Internal Program Version: SANE-Backends  1.2.1

USB scanner autoconfiguration happens via udev.

The file /etc/udev/rules.d/56-sane-backends-autoconfig.rules contains
entries for those USB scanners where the USB IDs are known, which are
supported by a free driver, where the support status is "complete" or
"good", and which do not require firmware upload.

When a USB scanner is connected and its USB IDs match to an entry in
the 56-sane-backends-autoconfig.rules file, the matching scanner driver
is activated (i.e. the driver line in /etc/sane.d/dll.conf is
activated).

It enables scanner drivers but never disables them. The reason is that
enabled drivers do not hurt so that an automated disable would make it
only overcomplicated because when more than one scanner uses the same
driver, a complicated check would be needed to avoid that the driver is
accidentally disabled when only one scanner was disconnected.

If you do not like automated driver activation, do not install this
package or remove it when it is already installed.

http://www.sane-project.org