PHP is a server side language and therefor what you are wanting is not possible with PHP alone. If a web page that has images on it is viewed, inherently the graphics have already been downloaded (that's why you see them). As for downloading pages, well... isn't that what the web is all about. No really, I assume you mean them downloading the actual source code... If it's PHP, it will run and they will only see the output, not the actual code itself. Also, even when the right-click is disabled, one can still copy whatever they want from the page. CTRL+INSERT works to copy and so does CTRL+C. All they need to do is highlight and press those buttons.
Sorry but the closest solution will be JavaScript and even that can't guarantee what you need.
AaronZoller.com
