The apparatus represents a device having one or two sensors for capturing a
single image or two images having the subject's eyes, in which a dimension, such as the
horizontal axis, with respect to pixels in the
single image or two first images characterizing zero
head tilt, and processors in one or more of a housing with the one or two sensors or in a computer
system which receives the
single image or two images. Such processors determine a
head tilt angle between a virtual line extending between the two eyes of the subject in accordance with predefined features, such as
pupil or iris center, in the single image or two images and the dimension characterizing zero
head tilt, segment left and right iris images from the single image or two images, and rotate the segmented left and right
iris image in accordance with the angle to substantially remove head tilt when present. A
database of identification data may be provided storing at least templates representative of right and left irises of a plurality of subjects without substantial head tilt, and the processors generate template(s) representative of the left and right irises of the subject, which are either added or compared to the identification data. The processor may also determine
interpupillary distance (IPD) or IPD-to-iris ratio using the single image or two images, and as such may be used for comparative searching of the identification data having IPD or IPD-to-iris ratio of the plurality of subjects.