Wigs, glasses, hats, or beards don't affect the identification process, which primarily scans the distance between the eyes and nose. The retina of the eye or iris , like fingerprints, is unique to each individual. The systems that read retinal and iris information test out as the most accurate, not to be foiled by false eyes, contact lenses, or eye transplants. But apparently users feel quite uncomfortable with this technology which is considered too much of an invasion upon one's privacy. Also, the identification data for these scans requires a good deal of system storage space.
Voice recognition is another method of identification.
It relies on cadence, pitch, tone, and the shape of larynx. This one works well in conjunction with other technologies because it's not as accurate as, say, fingerprints or iris scans. Background noise greatly affects how well the system operates, and users must speak at the appropriate time and in a clear voice to obtain a correct reading. However, voice recognition has been used successfully for verification over telephone lines, for example when a customer calls in to check account information. Signature verification is just what it sounds like.