How to change windows default Log in/out screen through a .Net application?

I want to write a .Net framework application which(after installation) can change the windows default Log in/out screens with my own pictures. Please help me how can i start it in .Net(any idea will help me a lot). Should i work with Windows forms/service or some else? I know one can change that screens directly from windows OS but i dont want to use that.

I'm very thankful for your replies, Actually I want to build an interactive application for Windows Logon Screen. The scenario is... Lets the system is locked, a person(not the system user) comes and he should be able to write some comments on Logon screen Textbox without getting log into system. When an administrator log into the system开发者_开发技巧(using Ctrl+Alt+Del and Password) he can read/print those comments. So how to start such application in .net using C#?

Assuming you want to do it on windows 7 you can achieve it this way

1- Create this key in registry

[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Authentication\LogonUI\Background]
"OEMBackground"=dword:00000001 

2- Create this path if does not exist

C:\Windows\System32\oobe\info\backgrounds

3- Copy a jpeg file named backgroundDefault.jpg with a size less than 256 KB to the aforementioned path.

4- Reboot.

You can do all this in any language,even with a simple batch file.

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In response to the updated question...

Actually I want to build an interactive application for Windows Logon Screen. The scenario is... Lets the system is locked, a person(not the system user) comes and he should be able to write some comments on Logon screen Textbox without getting log into system. When an administrator log into the system(using Ctrl+Alt+Del and Password) he can read/print those comments. So how to start such application in .net using C#?

This will not be possible. You cannot write a custom Windows login screen using C# or the .NET Framework. You will need to write unmanaged C++ code to implement such functionality.