>>After all the placement could easily be a foot or so off.<<
Maybe an inch or two, but nowhere near a foot — at least not if the chain crew is remotely competent. There is a clip that is placed on the chain at the location of the backside of the yard line, nearest to the first down spot stick. When the Head Linesman goes back to retrieve the chains for a measurement, he goes to the clip, brings the chains out, and then places the chain down at that same yard line. The Umpire takes the line to gain stick and pulls it tight for the measurement, a determination the Referee makes. Even with the stick and the ball right next to each other, sometimes it is VERY close and a picture several feet away will not always show whether the tip of the ball is even with the stick.
Read what I said again. I am not talking about the chain crew but about the ref’s placement after each play. That can be and often is off a foot or more.
Actually I am surprised how well they often do place the ball but when you just look at what you think is forward progress and spot the ball based on that it has to be just an estimate.