As the demand for security systems is increasing exponentially day by day, there has been a rigorous search for different verification and identification techniques. Facial features, voice patterns, hand geometry, retinal patterns, vein patterns, signature dynamics, voice verification, facial thermography, DNA matching, nailbed identification, gait recognition, ear shape recognition and finger prints have all been explored as biometric identifiers with varying levels of success. However, they have their own shortcomings. But iris has unique patterns; no two iris patterns are alike. After a rigorous review of hundreds of papers on iris recognition systems we present this review paper.

An ocean of information with unlimited expanse and unfathomable depth has been created and is made accessible to all human beings such that their knowledge could grow. Even if the ocean of information is available, only a small drop of this ocean which is appropriate for the specific event, is the requirement of the day. Thus, picking the drop that quenches our thirst is the current field of research as the ocean of database is increasing day by day. The curse of e-wars in all the e-systems calls for more and more secure systems and protection of data. Password-based security systems are almost cracked by the use of encryption and decryption techniques. Hence the researchers have focused their attention on the secure biometric systems. Biometrics like fingerprints, facial features, voice patterns, hand geometry, retinal patterns, vein patterns, signature dynamics, iris, etc., are being used. Of all the biometrics, iris has been proved to be the unique one. Iris as an identifier has been developing since 1997 (Williams, 1997). The uniqueness of iris patterns was identified ever since. This property of iris can be quoted in the words of Daugman (1993) as, "Advantage of the iris shares with fingerprints is the chaotic morphogenesis of its minutiae. The iris texture has a chaotic dimension because its details depend on initial conditions in embryonic genetic expression; yet the limitation of partial genetic penetrance (beyond expression of form, function, color and general textural quality), ensures that even identical twins have uncorrelated iris minutiae. Thus the uniqueness of every iris, including the pair possessed by individual, parallels the uniqueness of every fingerprint regardless of whether there is a common genome."

The main motivation of this paper is the guarantee assured by the iris as a lifelong and unique password. Biometric-based personal identification methods have recently gained more interest with an increasing emphasis on security. Color not only adds beauty to the object but also gives more information which is used as the powerful tool in object recognition as proposed by Kokare et al. (2002). Typical characterization of color composition is done by color histograms as proposed in the previous work of Lenina et al. (2006). A number of researchers having intensely worked on color as feature for recognition, for example Swain and Ballard (1991) proposed the method called color indexing, which identifies the objects using color histogram indexing. Color histograms are a way to represent the distribution of colors in images where each histogram bin represents the color in a suitable color space (RGB etc.) as proposed by Gonzalez and Woods (1992). An image of iris is shown in Figure 1a. A front-on view of the human eye is shown in Figure 1b.

Electrical and Electronics Engineering Journal, Iris Recognition, Biometrics, Features, Database, Wavelets, Histograms, Phase, Shape, Texture, Color, Transform, Content-based Image Retrieval, Iris Recognition Technology, Machine Readable Passport, MRP, Public Key Infrastructure, PKI, Forensic Application, Support Vector Machine, SVM, National Television Systems Committee, NTSC, Direct Linear Discriminant Analysis, DLDA.