Combined with Face2Face[1] live video impersonation, it is truly time to be very careful verifying videos or even live streams.
You are right that we'll have to worry about this soon though. Likewise, verifying the identify of people we think we're talking to over video calls for example.
...Is it normal to feel bad for the Johnnycab "driver" when Arnie destroys it?
Books like "Trust Me, I'm Lying" reveal the lengths at which deception can occur. Though this book discusses deception that starts at the textual level (e.g. blogs), it is inevitable that these tactics will be translated to the video level once the technology catches up.
Also, "at face value" - Ha! ;)