1. A method comprising: receiving, by a computing device, an authentication image; determining, by the computing device, whether a number of pixels positioned between at least two landmarks represented in the authentication image exceeds a threshold number of pixels; and responsive to determining that the number of pixels positioned between the at least two landmarks represented in the authentication image exceeds the threshold number of pixels, denying, by the computing device, authentication with respect to accessing one or more functionalities controlled by the computing device.