How do I keep people on the Internet from right-clicking and taking my pictures?

One question that turns up occasionally in class is "How do I keep people on the Internet from right-clicking and taking my pictures?"  One way to do this is to place a transparent image over the image you want to protect.  Whenever someone right-clicks your picture, the transparent one will be the one that is pasted.  Unfortunately, some picture stealers are persistent, and there's no way (that I know of) to completely prevent someone from taking your pictures.  For that reason, be very careful what you put out there!