How come some people's faces are blurred on hidden camera shoes and some aren't?

Question

How come some people's faces are blurred on hidden camera shoes and some aren't?

Answer 1

People who don't give their permission to be shown have their faces blurred out to protect their privacy. Everybody whose face you can see has given their permission to be shown.

Answer 2

Everyone who appears on television has to sign an appearance release form (you can see one here http://i.current.com/pdf/release.pdf ).  If producers are unable to get a release form signed by the person in the show, then they'll usually solve this problem by blurring the person's face.  

On many hidden camera shows, they probably approach the person afterward and ask them to sign the release form, because it's funnier if you can actually see the person's face.