Unless one has conducted a thorough genealogy of a particular actor / actress or done a DNA test, how does one know if a particular actor / actress is completely non-Jewish?

And if a hypothetical actor / actress is mixed Jewish, what is the proper percentage / lineage (e.g. matrilineal)?

That photo looks good. Mirren doesn't tend to disappear into a role like Meryl Streep or Alex Guinness, but her expression in that photo seems respectful (i.e. she's not playing to any kind of Jewish stereotype). There's nothing "Jewfacish" about it as far as I can tell. Laurence Olivier's makeup for Othello, on the other hand.....