The scanner group seems to be of no use in this case, the lp group on the other hand hit the spot as far as I can see.
When I run these commands as root:
found USB scanner (vendor=0x03f0 [Hewlett-Packard], product=0x2911 [PSC 2200 Series]) at libusb:001:004
device `hpaio:/usb/PSC_2200_Series?serial=MY27RD14D60G' is a Hewlett-Packard PSC_2200_Series all-in-one
As an ordinary user I get nothing from sane-find-scanner.
Scanning works perfectly as root.
Tried to add the user to the scanner group, to no avail.
Any tips where I should change permissions to make scanning as an ordinary user to work? I have an /dev/usb/lp0 entry, but changing the group of that to users (with r/w) does not help.