This is a most widely used iris recognition algorithm as of 2008. This is a version of the Daugman algorithm. It differs from an earlier version, “bowtie,” in the way it handles eyelid (and other) occlusions. The bowtie algorithm analyzed a bowtie shaped section of the iris – two triangular wedges extending to the left and right – that avoided most eyelid occlusion at the expense of throwing away information for eyes that are wide open. Iris2pi attempts to analyze all the iris that can be seen – a full 2π radians if possible. Iris2pi note regions that are occluded or otherwise invalid for biometric identification; it records that information in the biometric template. When two templates are compared, the algorithm only compares regions that have valid data.