/etc/sane.d/v4l.conf is in libsane 1.0.23-3ubuntu3.
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 10 11 12 | #
# In order to use the v4linux backend you have to give the device
# You can enable multiple lines if
# you really have multible v4l devices.
# Backends disabled, to re-enable unquote the following lines
# See https://bugs.launchpad.net/ubuntu/+source/sane-backends/+bug/87312
#/dev/bttv0
#/dev/video0
#/dev/video1
#/dev/video2
#/dev/video3
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