Face replacement in a Live Video

Hello i have a project where i must realize a live video with face detection and replace the face in the live video with a face in a image. It should be like the Snapchat face replacement. But i dont know really how i should start. I think, i can use the matlab builtin face detection and need feature points but i dont have an idea how i can replace the face in the video with an face in a image. I found here replacement with image to image or video to video but this dont help me. Have someone a idea or an example for me that would be great!!

[Yasir Codur]

I need really help, can never one help me?