blur a face to hide identity?

[mwatch]

Sometimes when watching a video you can see where they blurred/digitized a persons face to hide their identity. How do they do that? Can we do that at home with iMovie or Final Cut Express?

[Dr. Dastardly]

You have to make them sit down and watch this creepy video, but leave the room or you die in 7 days. :eek:

Isn't there a radius blur you can use in FCP that can do this. I do beleive there are tools that can be downloaded to do this though. Have you tried Google?