1. A computer-implemented method performed in connection with a computerized system comprising a processing unit, a camera and a memory, the computer-implemented method comprising: a) using the camera to acquire a plurality of images of a mobile computing device held by a user, the mobile computing device displaying a marker pattern; b) using the processing unit to detect the marker pattern within the acquired plurality of images; c) using the processing unit to determine a plurality of positions of the mobile computing device based on the detected marker pattern within the acquired plurality of images; d) using the processing unit to determine at least one characteristic of the marker pattern detected within the acquired plurality of images; e) determining presence of a pen up state or a pen down state based on the determined at least one characteristic of the marker pattern; and f) processing a user event based on the determined plurality of positions of the mobile computing device, wherein the processing the user event comprises rendering an ink stroke based on the determined plurality of positions of the mobile computing device if the pen down state is present.