Every race is a simulation driven by one number, the seed. Before post time we publish a fingerprint (SHA-256 hash) of that seed. After the race we reveal the seed, and anyone can check that it matches the fingerprint and replay the exact race.
In the live version the seed comes from the first Bitcoin block mined after picks close, so the result cannot be known in advance by anyone, including the track.
This demo uses a race that has already been rendered, so here the seal shows how verification works rather than proving fairness.