NASCAR uses two high-speed cameras to determine race resultsNASCAR used two high-speed photo cameras focused on the start-finish line to determine the finish. They take photos at about 6,000-8,0000 frames per second when any car crosses the finish line.
Source: NASCAR uses two high-speed cameras to determine race results (https://www.foxsports.com/watch/fmc-aryzyy26zyk3xuo8)