Sample Images can be Independently Restored from Face Recognition Templates

Biometrics promise the ability to automatically identify individuals from reasonably easy to measure and hard to falsify characteristics. They are increasingly being investigated for use in large scale identification applications in the context of increased national security awareness. This paper addresses some of the security and privacy implications of biometric storage. Biometric systems record a sample image, and calculate a template: a compact digital representation of the essential features of the image. To compare the individuals represented by two images, the corresponding templates are compared, and a match score calculated, indicating the confidence level that the images represent the same individual. Biometrics vendors have uniformly claimed that it is impossible or infeasible to recreate an image from a template, and therefore, templates are currently treated as nonidentifiable data. We describe a simple algorithm which allows recreation of a sample image from a face recognition template using only match score values. At each iteration, a candidate image is slightly modified by an eigenface image, and modifications which improve the match score are kept. The regenerated image compares with high score to the original image, and visually shows most of the essential features. This image could thus be used to fool the algorithm as the target person, or to visually identify that individual. Importantly, this algorithm is immune to template encryption: any system which allows access to match scores effectively allows sample images to be regenerated in this way.