I was asked by The Ripper, “I want to be able to pick the thumbnails used on YouTube. I’ve tried the math tricks for picking You Tube Thumbnails and they don’t work. How do you do it?”
Well Ripper, YouTube has made it hard for me to analyze this process completely by not allowing duplicate video uploads, but I did learn a good bit. And, I did find a way to increase the odds that you get a nice YouTube Thumbnail or Poster Frame using some common sense.