A small and little-discussed addition to the Sharing preference pane in Snow Leopard is a Scanner Sharing option, which lets your Mac share certain USB-attached scanners over the network in the same way as it can share a printer. (Leopard also supports scanner sharing, but using an entirely different procedure, as I explain later.) As with printer sharing, scanner sharing assumes you've already connected a scanner to your Mac and configured it in the Print & Fax pane of System Preferences.
Many, but not all, USB scanners are supported. To see a list of the scanners for which Snow Leopard includes drivers, see http://support.apple.com/kb/HT3669.
With a scanner configured and turned on, you can share it by following these steps if you're running Snow Leopard (instructions for Leopard appear later):
Choose System Preferences to open System Preferences and then click Sharing to open the Sharing pane.
If the lock icon in the lower-left corner of the pane is in the locked state, click it, type an administrator's username and password, and then click OK.
In the list on the left, click the On check box next to Scanner Sharing. Your scanner immediately becomes available on the network. With Scanner Sharing selected from the list on the left, as shown in Figure 7.9 ...