Face veins

ID got you, under the skin (Phys.org)

Ayan Seal and colleagues have developed a computer algorithm that can analyze the minutiae of the blood vessels revealed by an infra-red scan of a person's face. The thermogram readily reveals the pattern of blood vessels almost down to the smallest capillary with an accuracy of more than 97%. Such a degree of precision would suffice even for high-security applications provided the thermogram scan was tied to second or third forms of identity, such as photo ID, security card, PIN number etc.

A biometric modality depending of the vasculation of the face is an interesting idea because unlike most novel biometric modalities, face biometrics and vascular biometrics are fairly well understood.