/etc/sane.d/rts8891.conf is in libsane-common 1.0.25+git20150528-1ubuntu2.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 | # rts8891.conf: Configuration file for the rts8891 backend
# MODEL
# HP scanjet 4400c
usb 0x03f0 0x0705
# HP scanjet 4470c
usb 0x03f0 0x0805
# UMAX Astra 4400/4450
usb 0x1606 0x0070
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