It is often desirable to restrict access to property or resources to particular individuals. Biometric systems can be used to authenticate the identity of an individual to either grant or deny access to a resource. For example, iris scanners can be used by a biometric security system to identify an individual based on unique structures in the individual's iris.
In a typical image-based biometric authentication system, one or more images are obtained from a person claiming to be an authorized user. Those images are compared with one or more reference images that are known to be provided by one or more authorized users. Only if the claimant-supplied images match well with one or more reference images, the claimant can be determined to be an authorized user. A match between two images, i.e., a measure of similarity between the two images, can be based on features of those images. The features can include a collection of one or more points of interest in the image, and descriptions of portions of the image surrounding such interest points.