Fandome offers a fascinating 3 1/2 minute video explaining how the first-down line on football broadcasts* actually works. Evidently, there's a lot of processing to calculate the exact location being photographed on the field, and a lot more to draw a line in exactly** the right place.
*In American football, a team is allotted four plays to advance the ball at least 10 yards total, where a yard is approximately .9 meters. If it achieves this, it is said to have gotten a "first down."
**Actually, football fans often claim that the line is off by a foot or two now and then.
Edit: A longer, several-years-old (I think) write-up makes further points:
Some of the details in that article differ from those in the video, but the general idea is the same.
Curt Monash is a leading analyst of and strategic advisor to the software industry. Praised by Lawrence J. Ellison for his "unmatched insight into technology and marketplace trends," Curt was the software/services industry's #1 ranked stock analyst while at PaineWebber, Inc., where he served as a First Vice President until 1987. He subsequently co-founded Evernet, Inc., a $40 million networking systems integrator. Since 1990, he has owned and operated Monash Research, an analysis and advisory firm covering software-intensive sectors of the technology industry. In that period he also has been co-founder, president, or chairman of several other technology startups.
Curt has served as a strategic advisor to many well-known firms, including Oracle, Microsoft, SAP, AOL, CA, and Netezza. Curt earned a Ph.D. in mathematics (Game Theory) from Harvard University. He has held faculty positions in mathematics, economics and public policy at Harvard, Yale, and Suffolk universities.