Unfortunately you can't stop clients from copying the movie, unless you use an encrypting program (more below), however here are some options to think about:

1. Charge more for the first copy and a lot less for extra ones to encourage them to buy more copies from you at the same time.
   
   
2. If the slideshow is just to show the proofs, then add a copyright stamp or water mark to the slideshow images (ProSelect will do this for you) and/or produce it in a smaller size. See the ProSelect Reference Manual for more on Exporting a Slideshow and on Stamps (quick access under the Help menu in ProSelect).

And see this article "Preventing clients from copying images in a movie".

Hint:
Another Option is using an encrypting program such as "Flip album Pro" (available at the time of creating this article). It encrypts the files so they can not be copied. And will also let you put an expiry date on the CD. It can still be copied but the expiry date goes with it and after that time they still can not open the album. A good incentive for them to bring the orders back.