The Receiver Operating Characteristic (ROC) curve is created by plotting the True Positive Rate (TPR) against the False Positive Rate (FPR) at various threshold settings. The Area Under the Curve (AUC) for the ROC curve is equal to the probability that a classifier will rank a randomly chosen similar pair (images of same people) higher than a randomly chosen dissimilar one (images from two different people) (assuming 'similar' ranks higher than 'dissimilar' in terms of similarity scores).