I have an Epson multifunction device connected to a Raspberry Pi running the latest Raspbian. As you can see in the output below, scanimage will only find my scanner if I sudo it, but sane-find scanner finds it just fine without sudo. I've checked that the device permissions are properly set... saned is a memeber of the lp group, which is the group of the USB device. What gives?
richard@raspberrypi ~ $ scanimage > image.pnm
scanimage: no SANE devices found
richard@raspberrypi ~ $ sane-find-scanner
...
found USB scanner (vendor=0x04b8, product=0x0839) at libusb:001:004
found USB scanner (vendor=0x0424, product=0xec00) at libusb:001:003
...
richard@raspberrypi ~ $ sudo scanimage > image.pnm
richard@raspberrypi ~ $ sudo su -s /bin/bash - saned
X11 connection rejected because of wrong authentication.
No directory, logging in with HOME=/
saned@raspberrypi:/$ lsusb
Bus 001 Device 002: ID 0424:9512 Standard Microsystems Corp.
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 001 Device 003: ID 0424:ec00 Standard Microsystems Corp.
Bus 001 Device 004: ID 04b8:0839 Seiko Epson Corp. CX8300/CX8400/DX8400
saned@raspberrypi:/$ ls -l /dev/bus/usb/001
total 0
crw-rw-r-T 1 root root 189, 0 Feb 12 02:23 001
crw-rw-r-T 1 root root 189, 1 Jan 1 1970 002
crw-rw-r-T 1 root root 189, 2 Jan 1 1970 003
crw-rw-r--+ 1 root lp 189, 3 Feb 12 02:24 004
saned@raspberrypi:/$ groups
saned lp scanner