1. A method of performing a biometric function, the method comprising: illuminating a purported skin site of an individual with illumination light, wherein the purported skin site is in contact with a surface; receiving light scattered from the purported skin site, wherein the light is received substantially in a plane that includes the surface; forming an image from the received light; generating an image-texture measure from the image; and analyzing the generated image-texture measure to perform the biometric function.