A wireless phone is equipped with a 2D optical sensor, enabling a variety
of applications. For example, such a phone may also be provided with a
digital watermark decoder, permitting decoding of steganographic data on
imaged objects. Movement of a phone may be inferred by sensing movement
of an imaged pattern across the optical sensor's field of view, allowing
use of the phone as a gestural input device through which a user can
signal instructions to a computer-based process. A variety of other
arrangements by which electronic devices can interact with the physical
world are also detailed, e.g., involving sensing and responding to
digital watermarks, bar codes, RFIDs, etc.