This paper describes pattern processing and recognition for a user interface with real papers rather than display, keyboard and mouse for document editing. We call this UI (User Interface) as 'Paper based User Interface.' In order to realize this UI, we need a technology to detect and recognize correction marks written on printouts of documents. This paper presents a new technology that detects handwritten marks without restricting the way to write correction marks or forcing the users to use a pen of a specific color and a specific scanner. At first, documents are printed out with dotted characters, and they can be easily dropped out to detect correction marks and also they can be easily emphasized to detect where each correction mark is applied. We made a prototype on a PC and verified that the method can extract almost all correction marks correctly.