A method of authenticating a finger of a user against a stored template and expanding the stored template, comprising the steps of: acquiring a present partial candidate fingerprint image; retrieving a stored enrolment representation for said user, the stored enrolment representation comprising said stored template, and stored representations of a plurality of previous partial candidate fingerprint images (22a-f) acquired in connection with previous failed authentication attempts for said user; determining if a first match between a representation of the present partial candidate fingerprint image and said stored template fulfills a first template updating requirement indicating that the present partial fingerprint image is sufficiently similar to the fingerprint image represented by the stored template for template updating to take place and that authentication can be considered successful; determining if a second match between said representation of the present partial candidate fingerprint image and at least one of said stored representations of the plurality of previous partial candidate fingerprint images (22a-f) fulfills a second template updating requirement; when it is determined that said first match fulfills said first template updating requirement and said second match fails to fulfill said second template updating requirement: providing a signal indicating a successful authentication; and forming a first expanded template by expanding said stored template with said present partial candidate fingerprint image; when it is determined that said first match fulfills said first template updating requirement and said second match fulfills said second template updating requirement: providing a signal indicating a successful authentication; and forming a first expanded template by expanding said stored template with said present partial candidate image and said at least one stored representation of the plurality of previous partial candidate fingerprint images (22a-f); and when it is determined that said first match fails to fulfill said first template updating requirement: providing a signal indicating failed authentication; and forming an updated enrolment representation by adding said representation of the present partial candidate fingerprint image to said stored enrolment representation as a previous partial candidate fingerprint image. acquiring a present partial candidate fingerprint image; retrieving a stored enrolment representation for said user, the stored enrolment representation comprising said stored template, and stored representations of a plurality of previous partial candidate fingerprint images (22a-f) acquired in connection with previous failed authentication attempts for said user; determining if a first match between a representation of the present partial candidate fingerprint image and said stored template fulfills a first template updating requirement indicating that the present partial fingerprint image is sufficiently similar to the fingerprint image represented by the stored template for template updating to take place and that authentication can be considered successful; determining if a second match between said representation of the present partial candidate fingerprint image and at least one of said stored representations of the plurality of previous partial candidate fingerprint images (22a-f) fulfills a second template updating requirement; when it is determined that said first match fulfills said first template updating requirement and said second match fails to fulfill said second template updating requirement: providing a signal indicating a successful authentication; and forming a first expanded template by expanding said stored template with said present partial candidate fingerprint image; providing a signal indicating a successful authentication; and forming a first expanded template by expanding said stored template with said present partial candidate fingerprint image; when it is determined that said first match fulfills said first template updating requirement and said second match fulfills said second template updating requirement: providing a signal indicating a successful authentication; and forming a first expanded template by expanding said stored template with said present partial candidate image and said at least one stored representation of the plurality of previous partial candidate fingerprint images (22a-f); and providing a signal indicating a successful authentication; and forming a first expanded template by expanding said stored template with said present partial candidate image and said at least one stored representation of the plurality of previous partial candidate fingerprint images (22a-f); and when it is determined that said first match fails to fulfill said first template updating requirement: providing a signal indicating failed authentication; and forming an updated enrolment representation by adding said representation of the present partial candidate fingerprint image to said stored enrolment representation as a previous partial candidate fingerprint image. providing a signal indicating failed authentication; and forming an updated enrolment representation by adding said representation of the present partial candidate fingerprint image to said stored enrolment representation as a previous partial candidate fingerprint image.