Said Rabbi Shimon ben Lakish: The forehead exempts in all cases—except for inheritance.
What is the reason? As it is written, “He must recognise.”
But Rabbi Yohanan said: Even for inheritance.
“In all cases”—to include what?
To include this that our rabbis taught: A female convert [whose son’s] forehead comes out and she gives birth while still a Gentile, and afterwards she converts—they do not give her the days of her impurity or the days of her purity, nor does she bring a birth sacrifice.
They objected: “He must recognise”—this is facial recognition. And what is facial recognition? The distinctive features of the face with the nose!
He recited: Until the nose.
Come and learn: They do not testify [about a woman that she can get remarried after her husband’s death] except based on [seeing the husband’s] distinctive features of the face with the nose!
He recited: Until the nose…
Testimony for a wife is different since the rabbis were stringent on it…
Or if you want, another answer: “He must recognise” and “facial recognition” are unrelated laws.