As with most other biometric identification technology, an important consideration is live-tissue verification. The reliability of any biometric identification depends on ensuring that the signal acquired and compared has actually been recorded from a live body part of the person to be identified and is not a manufactured template. Besides a person's physical characteristics, which includes the eyes, one's voice and handwriting too, are not protected by the Fourth Amendment even though they are all constantly exposed. Many commercially available iris-recognition systems are easily fooled by presenting a high-quality photograph of a face instead of a real face, which makes such devices unsuitable for unsupervised applications, such as door access-control systems. However, this is not the case with all iris recognition algorithms. The problem of live-tissue verification is less of a concern in supervised applications (e.g., immigration control), where a human operator supervises the process of taking the picture.