Lexmark tech support pointed me at SANE documentation, but I'll confess feeling quite lost in it.
When I run XSANE it says "no devices available". Running it as root user, same result (after the scare dialog).
This is the output for same-find-scanner, as a regular user and then as root:
rafu@Anatrone:~$ sane-find-scanner
#sane-find-scanner will now attempt to detect your scanner. If the
#result is different from what you expected, first make sure your
#scanner is powered up and properly connected to your computer.
#No SCSI scanners found. If you expected something different, make sure that
#you have loaded a kernel SCSI driver for your SCSI adapter.could not open USB device 0x8087/0x0020 at 002:002: Access denied (insufficient permissions)
could not open USB device 0x1d6b/0x0002 at 002:001: Access denied (insufficient permissions)
could not open USB device 0x275d/0x0ba6 at 001:003: Access denied (insufficient permissions)
found USB scanner (vendor=0x043d [Lexmark], product=0x0227 [Lexmark MX310dn]) at libusb:001:004
could not open USB device 0x8087/0x0020 at 001:002: Access denied (insufficient permissions)
could not open USB device 0x1d6b/0x0002 at 001:001: Access denied (insufficient permissions)
#Your USB scanner was (probably) detected. It may or may not be supported by
#SANE. Try scanimage -L and read the backend's manpage.
#Not checking for parallel port scanners.
#Most Scanners connected to the parallel port or other proprietary ports
#can't be detected by this program.
#You may want to run this program as root to find all devices. Once you
#found the scanner devices, be sure to adjust access permissions as
#necessary.
rafu@Anatrone:~$ sudo sane-find-scanner
[sudo] password for rafu:
#sane-find-scanner will now attempt to detect your scanner. If the
#result is different from what you expected, first make sure your
#scanner is powered up and properly connected to your computer.
#No SCSI scanners found. If you expected something different, make sure that
#you have loaded a kernel SCSI driver for your SCSI adapter.found USB scanner (vendor=0x043d [Lexmark], product=0x0227 [Lexmark MX310dn]) at libusb:001:004
#Your USB scanner was (probably) detected. It may or may not be supported by
#SANE. Try scanimage -L and read the backend's manpage.
#Not checking for parallel port scanners.
#Most Scanners connected to the parallel port or other proprietary ports
#can't be detected by this program.