If you just want to use a still, go into a picture editing program, and colour in everything else apart from your face green. Import that new picture into your editing program, and use chroma key to remove the green, leaving only your face. Stick this in another track from your video.

I have Pinnacle, and the way I would do this is to just keyframe the position of the head on the screen, so that it stays with the head of the person who is in the video.

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