I think you are looking for these drivers:
Epson Workforce 845 scroll about 1/3 of the way down on the page
Scanner Drivers here
According to the SANE web site
>>>>> found USB scanner (vendor=0x04b8, product=0x0892) at libusb:001:007 is your Epson scanner.
Time to edit:
gksudo gedit /etc/sane.d/epkowa.conf Example Snippet follows:
# epkowa.conf -- sample configuration for the EPKOWA SANE backend
# Copyright (C) 2004, 2008, 2009 Olaf Meeuwissen
# See sane-epkowa(5), sane-usb(5) and sane-scsi(5) for details.
# Detect all devices supported by the backend.
# If you don't have a SCSI device, you can comment out the "scsi"
# keyword. Similarly for the other keywords.
# For any USB scanner not known to the backend (yet), you may, at your
# own peril(!!), force the backend to recognise and use it via libusb.
# You can do so by the following configuration command:
# usb <USB vendor ID> <USB product ID>
# SEIKO EPSON's USB vendor ID is '0x04b8' (without quotes). In order
# to find the USB product ID, use lsusb(1).
# A sample configuration for the Epson Perfection 1650 (Epson GT-8200),
# which has a product ID of 0x0110, would look as follows:
#usb 0x04b8 0x0110
you will need to insert (vendor=0x04b8, product=0x0892) per the example and remove the "#" at the beginning code line. Save and reboot.