1. A method for segmenting a biometric characteristic from an eye image captured by a biometric device, the eye image comprising a pupil image, an iris image, and a sclera image, and the method comprising the steps of: identifying an initial pupil boundary of the pupil image; applying a multiplicity of first search windows onto the eye image; identifying a refined pupil boundary of the pupil image based at least in part on the initial pupil boundary and a multiplicity of first search windows; identifying a center of the pupil image based at least in part on the refined pupil boundary of the pupil image; searching for a light-to-dark edge to the left of the pupil boundary to identify at least a first edge point between the sclera image and the iris image; searching for a dark-to-light edge to the right of the pupil boundary to identify at least a second edge point between the sclera image and the iris image; estimating an initial non-occluded iris outer boundary of the iris image based at least in part on the identified edge points and the center of the pupil image; applying a multiplicity of second search windows onto the eye image, the multiplicity of second search windows being based at least in part on the initial non-occluded iris outer boundary for the iris image; identifying a set of points corresponding to peaks in an image intensity gradient in each second search window of the multiplicity of second search windows; and defining a refined non-occluded iris outer boundary for the iris image based on the set of points.