How Can I Replace Windows Default Login With My Face Recognition Application To Login To My Pc?

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Windows

.NET

C#3.5

service

I am an undergratuate and i am doing my research project these days.I created the face recognition application using Emgu CV Library and in c# language. I want to run that application before windows default login window is appearing. Actually i want to replace windows login with my face recognition login. i tried to run my application exe using windows registry, group policy and task schedular.But all the time i got the application after startup screen is appeared. It is too late.
I want to do this task in windows 8 os. The main thing i want is ,
I power on the pc
then my face application is appearing.
When my face is recognized, as the default windows login i should be redirected to the desktop or startup screen.
I'm in a very critical situation so that i tried my best to do this but i couldn't. Any body around me even don't know how to do this.....
So if anybody can help me to overcome this problem i'm really really greatfull
Thank u..