Systems and methods that determine a path of a pen tip as the pen tip is moved across a document are described. The document is watermarked with a maze pattern from which encoded position information is determined. A sequence of images is captured by a camera that is located in a pen. The path of the...http://www.google.com.au/patents/US20080025612?utm_source=gb-gplus-sharePatent US20080025612 - Strokes Localization by m-Array Decoding and Fast Image Matching
