These attributes represent either learned behavior or natural properties. Methods depending on learned skills include the recognition of speech, handwriting, or keystroke patterns.
Natural properties cover the face, retinal texture, iris morphology, hand geometry, or fingerprints.
Obviously, methods based on gait, odor, or genetic composition using DNA are not yet practical for online systems. First, a vocal print is derived using three passwords that the user repeats three times at enrollment. Furthermore, prerecorded vocal messages may deceive the system. In handwriting recognition, the user writes on a special pad with a pressure-sensitive pen. One limitation of handwriting recognition is that the rate of false rejects may be too high.