Method of printed bill payment using optically imaging pen

A method of enabling payment of bills using an optically imaging pen, the method comprising the steps of:

• optically imaging a coded tag printed on a bill with an image sensor of the pen, the bill being printed with information on a requested payment and a plurality of coded tags, each tag encoding an identity of the bill and it's printed location;
• computing, in the pen, the position of a nib of the pen relative to the bill during said optical imaging from:
• the tag location identified in the imaged tag;
• an observed perspective distortion on the imaged tag;
• and a known spatial relationship between the pen's physical axis containing the nib and the pen's optical axis containing the image sensor, said axes being different from each other;
• generating, in the pen, indicating data indicative of the identity of the bill identified in the imaged tag and the computed position of the nib relative to the bill;
• and
• transmitting the indicating data to a computer system to enable payment of the bill therein.