Content authentication for printed images utilizing high capacity data hiding

Authentication of content in printed images poses a challenge that cannot be addressed by conventional digital signature schemes because under the analog transport provided by the printing channel the verifier does not have access to the original digital content in pristine form. We present a method for cryptography-based authentication of the content in printed images that also provides the capability for identifying localized changes made by informed malicious attackers-key functionality that is missing in print scan robust hashes that have traditionally been used for print content authentication. The proposed method operates by embedding, within the printed image, an authentication signature that consists of an encrypted thumbnail of the image using a high capacity data hiding method for halftone images. To authenticate the content, the embedded signature is extracted from a scan of the printed image and, after decryption, compared with the printed content. An implementation of the method that incorporates human or automated verification and identifies potential local tampering by informed malicious attackers is developed and successfully demonstrated. (C) 2013 SPIE and IS&T