Capture the active window to jpg using C#?

I am creating a Windows Application that capture the all users session details.

I want to track that how many users are connected with my machine using RDP session. Want to log all their activity with screen shot.

So I would like to know how can I capture the active screen. I tried 'RUNAS' but its show me curr开发者_JS百科ent screen shot where I run. I am able to use user's application data but not get Actual screen.

I also tried LogonUser, CreateProcessAsUser but not getting actual point. So please let me know how can I do it ?

I used 'cassia' google library to list all the current logged user.

Thanks Laxmilal

It would be far easier to cause your application to startup in the user's session when they log into the machine, and then monitor the user session its already in. The problems inherent in syncronizing several instances of your running application (one per user logged in) are much easier to solve then the problems involved in having an application punch through windows user sessions and run code in several different sessions at once (and then synchronize it all anyway).