Authenticating a user operating a portable computing device includes causing a sequence of images to be shown on a display, accepting an input selection from the user indicating that a currently displayed image of the sequence of images corresponds to a portion of the user's password, the user's password...http://www.google.com.tw/patents/US7337466?utm_source=gb-gplus-share專利 US7337466 - Information hiding through time synchronization
