sudo sane-find-scanner -v
This is sane-find-scanner from sane-backends 1.0.23

  # 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.

searching for SCSI scanners:
[snip]
  # No SCSI scanners found. If you expected something different, make sure that
  # you have loaded a kernel SCSI driver for your SCSI adapter.

searching for USB scanners:
checking /dev/usb/scanner... failed to open (Invalid argument)
checking /dev/usb/scanner0... failed to open (Invalid argument)
checking /dev/usb/scanner1... failed to open (Invalid argument)
checking /dev/usb/scanner2... failed to open (Invalid argument)
checking /dev/usb/scanner3... failed to open (Invalid argument)
checking /dev/usb/scanner4... failed to open (Invalid argument)
checking /dev/usb/scanner5... failed to open (Invalid argument)
checking /dev/usb/scanner5... failed to open (Invalid argument)
checking /dev/usb/scanner7... failed to open (Invalid argument)
checking /dev/usb/scanner8... failed to open (Invalid argument)
checking /dev/usb/scanner9... failed to open (Invalid argument)
checking /dev/usb/scanner10... failed to open (Invalid argument)
checking /dev/usb/scanner11... failed to open (Invalid argument)
checking /dev/usb/scanner12... failed to open (Invalid argument)
checking /dev/usb/scanner13... failed to open (Invalid argument)
checking /dev/usb/scanner14... failed to open (Invalid argument)
checking /dev/usb/scanner15... failed to open (Invalid argument)
checking /dev/usbscanner... failed to open (Invalid argument)
checking /dev/usbscanner0... failed to open (Invalid argument)
checking /dev/usbscanner1... failed to open (Invalid argument)
checking /dev/usbscanner2... failed to open (Invalid argument)
checking /dev/usbscanner3... failed to open (Invalid argument)
checking /dev/usbscanner4... failed to open (Invalid argument)
checking /dev/usbscanner5... failed to open (Invalid argument)
checking /dev/usbscanner6... failed to open (Invalid argument)
checking /dev/usbscanner7... failed to open (Invalid argument)
checking /dev/usbscanner8... failed to open (Invalid argument)
checking /dev/usbscanner9... failed to open (Invalid argument)
checking /dev/usbscanner10... failed to open (Invalid argument)
checking /dev/usbscanner11... failed to open (Invalid argument)
checking /dev/usbscanner12... failed to open (Invalid argument)
checking /dev/usbscanner13... failed to open (Invalid argument)
checking /dev/usbscanner14... failed to open (Invalid argument)
checking /dev/usbscanner15... failed to open (Invalid argument)
could not fetch string descriptor: Pipe error
could not fetch string descriptor: Pipe error
could not fetch string descriptor: Pipe error
could not fetch string descriptor: Pipe error
  # No USB scanners found. If you expected something different, make sure that
  # you have loaded a kernel driver for your USB host controller and have setup
  # the USB system correctly. See man sane-usb for details.

  # Not checking for parallel port scanners.

  # Most Scanners connected to the parallel port or other proprietary ports
  # can't be detected by this program.
done