[ckissick]

As for football games, they first accurately survey the locations of the cameras in relation to the field. Once the precise locations of the cameras and the field are known, a computer simply overlays digital yard markers onto the field.

It only puts the image onto a green background so the lines don't go through jerseys and the ball. It has to be a specific shade of green so the lines don't go through the jerseys of the Eagles. I've noticed the line on jerseys where there is a good grass stain.