You can put all of the script in the site that you want, but you can't escape the print screen button. If a user wants to steal the image bad enough, they'll find a way to get it. Your safest bet if you're trying to run an e-commerce site would be to put watermarks on all of the images (which you can do from code in most languages so you don't have to modify each image manually). Then you can offer a download link for the customer once the image has been paid for that expires after so long so they can't give it to all of their friends.
Here are a couple of resources on how to do this in some various programming languages.
ASP.NET VB
http://articles.techrepublic.com.com/5100-10878_11-6131225.html
ASP.NET C#
http://www.codeproject.com/KB/GDI-plus/watermark.aspx
PHP
http://www.sitepoint.com/article/watermark-images-php
http://www.devshed.com/c/a/PHP/Dynamic-Watermarking-with-PHP/
If you need any help implementing these in your solution, because posting a full walk-through on how to use these scripts would be outside the scope of this post, feel free to pm me or contact me via e-mail.