2 ways 1 way has been made public which is wrinkle mapping. The other is forensic audio analysis.
Additionally, you seem to think proving he is fake is on pare with proving he is real. It is not. Technically I don't need to prove he is the same, you need to prove he is not. But I will show it anyway.
Plastic surgeon Dr. Steven Davis told OK in October of 2020: "Joe Biden definitely had a facelift. "After reviewing photos over the years the scars along the ear cartilage (tragus) are being pulled outward... most likely at least a year or so old."
Dr. Barry Cohen, a Washington DC plastic surgeon, told the Washington Examiner: "Without any question, Joe Biden had hair transplants. In fact, he had bad plugs years ago."
"Subsequently, he filled in his frontal hairline to camouflage the bad 'Barbie doll-esque' plugs."
"I suspect he has regular Botox and probably filler. If he had a facelift, he needs another."
Cohen said that he did not expect Biden to face scrutiny for his procedures because they are now common. He added: “No one cares anymore."
Prove it's the same Biden.
Additional info