Determined users can still get your images by File > Save As or by looking
at their browser cache or by View > Source.
Having said that, here are a few scripts that can help:
Disable right mouse click script II (on images) http://www.dynamicdrive.com/dynamicindex9/noright2.htm
(Remove the line "alert(clickmessage);" to improve the right-click
protection mechanism, as a user can press and hold the right mouse button,
press enter to the alert, and release the button to show the menu)