Anil K. Jain et.al  reviews about the biometric system is viewed as signal detection system with pattern recognition architecture. The biometric signal is sensed with an extraction salient set of features and compares them against the feature sets residing in the database. It validates an identity or determines the associated signal. The sensing unit consists of a biometric sensor which it scans the biometric characteristic of an individual to produce a digital representation of the characteristic. Here the quality check is generally performed to ensure the acquired sample to be reliably processed by the successive stages. To facilitate matching, the digital input representation is further processed by the feature extractor to generate a compact. Here the feature set can be stored as a template for the future comparison. The feature set will pulling out the irrelevant and needless information from the sensed dimensions and gleans the useful information essential for matching.
Examples of biometric characteristics
(a) Face, (b) fingerprint, (c) hand geometry, (d) iris,
(e) Keystroke, (f) signature, and (g) voice.
If the biometric characteristics of face, iris, finger and voice got any damage by means, then the system will not authenticate the user to communicate with the server. In this approach the major drawback is that such systems can be more expensive, and the identification process can be slow and often unreliable.
R. Dhamija and A. Perrig  reviews about the projected method to improve the security of the systems based on recognition and recall based authentication schemas. The recognition based authentication system is used to authenticate a user through their ability to recognize the earlier seen images. The recall based scheme is more consistent and easier for the user to remember the accurate passwords or PINs. In this technique, the user is asked to select a certain number of images from the given set of random pictures that will be generated by the program. Then the user will be authenticated by means of identifying the preselected images.
This technique fails to impress because in the server it has to store the seeds of the portfolio images of each user in plain text format, and the images will remain the same for all login sessions. The major drawback of this approach is that users spent more time on browsing to create image portfolios than to create passwords and PINS.
Ziran Zheng et.al  reviews about that the graphical password schemes has been considered as alternatives to text password, it has some drawbacks to shoulder-surfing and guessing attacks on because of the users straight actions upon the input screen. This method is anticipated to make a bridge between the graphic and text password. As the shape of the password cover larger space and easier to keep in mind.