If you have connected a scanner to the server  but it is not accessible from client, this means that bug #219473 is still unsolved. For more information, see no policykit access on ltsp thin client.

Permanent Solution

Create a udev rule to set the device with the scanner group. Open your text editor and create, or open if it already exist, file named 42-local.rules in /etc/udev/rules.d/ . I use Gedit:

sudo gedit /etc/udev/rules.d/42-local.rules

Then add the new udev rule:

# This rule sets scanner's group to "scanner", allowing LTSP users to use the scanner on the server.

SUBSYSTEM=="usb", ATTR{idVendor}=="04a9", ATTR{idProduct}=="2220", SYMLINK+="%k", GROUP="scanner"

To find the idVendor and idProduct of your scanner use this command:

sane-find-scanner

It will give you the necessary information:

found USB scanner (vendor=0x04a9 [Canon], product=0x2220 [CanoScan], chip=LM9832/3) at libusb:001:018

For more information about how to create udev rules, read Writing udev rules.

Save the file and close Gedit. Reconnect your scanner or restart your PC. Log in on your client station and you are now able to use the scanner.

Temporary Solution

Quick hack - change the scanner's group from root to scanner. Thus all users who are allowed to use scanners will have access to it.

You can change the group using Nautilus. In the terminal on server run:

sane-find-scanner

This will show you what is your scanner location. In my case it shows:

found USB scanner (vendor=0x04a9 [Canon], product=0x2220 [CanoScan], chip=LM9832/3) at libusb:001:023

This means that I have to check the permissions of 023 file located in /dev/bus/usb/001/ directory. Type in terminal:

ls -l /dev/bus/usb/001

It will show this:

total 0
crw-rw-r--  1 root root    189,  0 2009-01-29 21:54 001
crw-rw-r--+ 1 root root 189, 22 2009-02-01 14:46 023

Open Nautilus as root:

gksudo nautilus

and change file's group to Scanner so that ls -l shows this:

total 0
crw-rw-r--  1 root root    189,  0 2009-01-29 21:54 001
crw-rw-r--+ 1 root scanner 189, 22 2009-02-01 14:46 023 

Note: This is a temporary solution until next restart. After each restart you need manually to change scanner's group.

I submitted a bug report to Bugs.LaunchPad.net - User on client cannot access scanner connected to server.