Preventing Screen Capture

Hi all
I was just wondering if there was anyway of preventing people from capturing a screen image..

You can disable the mouse context menu (normally the right mouse click - or left if you've swapped the default mouse options) on an image to stop people from downloading it but I don't think you can prevent anybody from using the PRT SCR button or programs like snagit or the snipping tool to capture an image.

I'd like to do this since I want to issue some powerpoint lecture notes containing some pictures of propietary material which can be publicly viewed -- but I don't want these pics to be copied and possibly appear on other web sites.

Some type of internal "scambling" or encryption software would be great so that even if one did capture the screen via PRT SCR then on inserting the capture into another document it would just come out as garbled.

Any ideas anyone or is this just not possible.

(Of course the old fashioned way of actually taking a photo of the screen would always overcome any software scrambling / encryption or even using the screen capture on a Linux host machine running a Window Guest Virtual machine in "Windowed mode" - but I'm not worried about that type of attack - if people think of that type of "get around" then they are sophisticated enough to copy the documents anyway).

Cheers
jimbo

(I'm actually seeing the 'disable right-click' menu being circumvented by using FF and not IE on many sites now.)