1. A method performed by a computing device of providing access to a protected resource, the method comprising: receiving, by the computing device, an authentication request from a user seeking access to the protected resource; in response to receiving the authentication request, generating a set of one or more face images, each face image of the set of face images having a facial expression score for a particular emotion associated with that face image, the facial expression scores being specific to the user; displaying each face image of the set of face images to the user together with a request for the user to score that face image for the particular emotion associated with that face image; in response to displaying each face image, receiving a user score for that face image; comparing the received user score for each face image of the set of face images to the respective facial expression score for the particular emotion associated with that face image, yielding a set of comparison results; and selectively providing access to the protected resource in response to each of the comparison results being affirmative.