I have a requirement of disabling the end users who remote desktop to a Server 2008 R2 machine to capture images digitally through say Print Screen key. Is there a reliable way to do it? I should mention that the remote desktop session runs in full screen mode so the user cannot use Snipping Tool from the client machine to capture the desktop screen. Snipping tool is also disabled on the Server.
The client can use snipping tool, even in full-screen. Even if you find a way to disable the print screen key on clients (You can if you have control of their registry, but that requires completely disabling the key and rebooting the client system. If people are remoting in with their own systems, that isn't going to happen), there are hundreds of screen-capturing utilities that can screenshot and record the RDP window as it is visible on their machine.
And, they can always take a picture with their smartphone. It sounds like you're trying to find a technical solution to a social problem - these almost never work out well.
Unless you're talking about a kiosk system where you have 100% full control of the client, and you have the resources to write a utility that prevents RDP from losing focus, then an RDP client can screenshot and record anything on the RDP session that they want.
Your requirement is not technically feasible. As a client user, I'm either authorized to view the data, or I'm not. If you can't trust what someone will do with the data, don't authorize them to view it at all.
If you have full physical security, then
The idea here is that:
This all breaks apart if the user can connect the machine to a different network or if they can physically touch the client machine itself (other than the mouse/keyboard).