as long as a person can Print Screen they can steal anything they can see on their screen, flash or no right click included.

Don't display samples of shoots until they've placed their order.
Don't do web proofing if at all possible, and if you do then watermark them and use a site that makes it more difficult to steal images, and don't upload hi res.

For HS seniors, the most likely to hurt me by stealing (money wise) I just include a CD of lo-res pics of what they buy in their package and tell them they're for MySpace or email or whatever they want.