I used to use a JS no-right-click gimmick, but I took that down.
A visitor emailed to ask why I was disallowing some other perfectly innocent function.
Paul in SA is right; virtually any browser nowadays can copy images at will, regardless.
What I do is search my access logs for hot-linked images with no page URL or credits.
Once in a long while I do a image searches to see if my images magically appear on other sites. - Larry