Detecting modifications in paper documents: a coding approach

This paper presents an algorithm called CIPDEC (Content Integrity of Printed Documents using Error Correction), which identifies any modifications made to a printed document. CIPDEC uses an error correcting code for accurate detection of addition/deletion of even a few pixels. A unique advantage of CIPDEC is that it works blind – it does not require the original document for such detection. Instead, it uses fiducial marks and error correcting code parities. CIPDEC is also robust to paper-world artifacts like photocopying, annotations, stains, folds, tears and staples. Furthermore, by working at a pixel level, CIPDEC is independent of language, font, software, and graphics that are used to create paper documents. As a result, any changes made to a printed document can be detected long after the software, font, and graphics have fallen out of use. The utility of CIPDEC is illustrated in the context of tamper-proofing of printed documents and ink extraction for form-filling applications.