Overlay a photo in Windows Movie Maker How do you add a picture on top of a video in Windows Movie Maker? I only know how to add text on top of the video.

I want to use an image to block a person's face in the video. How can I do that?

If that isn't possible, how can I blur the face out?
As Windows Movie Maker don't support multi track editing, I don't think it is possible to overlay images onto the main video. Similarly, I don't think it has the required features to blur a specific area. 
If you are looking for a software recommendation, Sony Movie Studio can do both of these things (£60), and so can Blender (free, but very hard to learn) 
Sorry not to have been more helpful.