There is disclosed a mobile device comprising a processing unit for executing a host application, a user-interactive display and an authentication unit; wherein the authentication unit is arranged to receive an authentication request from the host application; wherein the authentication unit is arranged to cause the display to show a set of pictures in response to receiving the authentication request; wherein the authentication unit is further arranged to identify a selection of at least one picture from said set of pictures; and wherein the authentication unit is further arranged to initiate a verification of said identified selection. Furthermore, a corresponding method of authenticating a user is disclosed, as well as a corresponding computer program, an article of manufacture and a display.