  One weakness of machine-learning algorithms is the need to train the models
for a new task. This presents a specific challenge for biometric recognition
due to the dynamic nature of databases and, in some instances, the reliance on
subject collaboration for data collection. In this paper, we investigate the
behavior of deep representations in widely used CNN models under extreme data
scarcity for One-Shot periocular recognition, a biometric recognition task. We
analyze the outputs of CNN layers as identity-representing feature vectors. We
examine the impact of Domain Adaptation on the network layers' output for
unseen data and evaluate the method's robustness concerning data normalization
and generalization of the best-performing layer. We improved state-of-the-art
results that made use of networks trained with biometric datasets with millions
of images and fine-tuned for the target periocular dataset by utilizing
out-of-the-box CNNs trained for the ImageNet Recognition Challenge and standard
computer vision algorithms. For example, for the Cross-Eyed dataset, we could
reduce the EER by 67% and 79% (from 1.70% and 3.41% to 0.56% and 0.71%) in the
Close-World and Open-World protocols, respectively, for the periocular case. We
also demonstrate that traditional algorithms like SIFT can outperform CNNs in
situations with limited data or scenarios where the network has not been
trained with the test classes like the Open-World mode. SIFT alone was able to
reduce the EER by 64% and 71.6% (from 1.7% and 3.41% to 0.6% and 0.97%) for
Cross-Eyed in the Close-World and Open-World protocols, respectively, and a
reduction of 4.6% (from 3.94% to 3.76%) in the PolyU database for the
Open-World and single biometric case.
