It is a basic grammatical rule that both the infinitive (to see, to have seen) and the gerund (seeing, having seen) can occur as the subject of a clause. Therefore, both are correct in your sentence. Native speakers don't often use the infinitive as the subject but prefer the gerund : Seeing is believing.
New words, one handy idiom, and a 2-minute quiz — delivered to your inbox to keep your streak alive.