School of Electronic Engineering, University of Electronic Science and Technology of China Chengdu 610054 China
Abstract The demand on security is increasing greatly in these years and biometric recognition gradually becomes a hot field of research. Iris recognition is a new branch of biometric recognition, which is regarded as the most stable, safe and accurate biometric recognition method. In these years, much progress in this field has been made by scholars and experts of different countries. In this paper, some successful iris recognition methods are listed and their performance are compared. Furthermore, the existing problems and challenges are discussed.
Key words biometric recognition; iris localization; normalization; feature vector extraction and match

Introduction
We are living in the age, in which the demand on security is increasing greatly. Consequently, biometric recognition, which is a safe, reliable and convenient technology for personal recognition, appears. This technology makes use of physiological or behavioural characteristics to identify individuals[1]. A biometric system is a pattern recognition system including acquiring the biometric feature from individual, extracting the feature vector from the raw data and comparing this feature vector to another person’s feature vector. Fingerprint, palm-prints, face, iris, gait, speech and signature are widely used biometric features. Biometric recognition can be used in computer network login, internet access, ATM, credit card, national ID card, driver’s license and so on[2]. Nowadays, fingerprint recognition is used widely and successfully. Face recognition is studied by many scholars and experts. Iris recognition is a relatively new branch of biometric recognition.
The human iris is the annular part between pupil and sclera. It has distinct feature such as freckles, coronas, stripes, furrows and so on[3]. An example of iris image is shown in Fig.1. Compared to other biometric technique, iris recognition has many merits:
1) Uniqueness: Dissector F. H. Adler suggested the uniqueness of iris originally in 1965. The visible features in an iris include the trabecular meshwork of connective tissue, collagenous stromal fibres, ciliary processes, contraction, and frekles[3-5]. These textures ensure that different persons have distinct iris. The probability of two persons’ irises being the same is lower than 10?35. Even though they are twins, their irises are quit different. This fact is the reason why we use iris to recognize personal identity.
2) Reliability: iris is an inner organ in our eyes and protected by eyelid, lash and cornea. Unlike finger and palm, it is seldom hurt and the error of recognition caused by scar will never happen. In this sense, iris recognition is much better than fingerprint and palm-print recognition. Furthermore, our irises matured when we were one year old and would not change in our life.
3) Against artifice: a living eye’s pupillary diameter relative to iris diameter in a normal eye is constantly changing, even under stead illumination. The pupillomotor response could provide a test against artifice.