Oops, hit send too quickly. :) That was supposed to say "as opposed to just having an image file which could easily be duplicated".

Rationale: you'd have a copy of that image file once I'd sent it to you, and chances are a few other people may have access to that image file, so verifying I actually had the real document would be somewhat important (though of course depending on the video quality this may not be a great solution as you might not be able to verify the document is the same one as in the image…)