Extrinsic Signature Embedding and Detection in Electrophotographic Halftoned Images Through Exposure Modulation

Abstract

Printer identification based on printed documents can provide forensic information to protect copyright and verify authenticity. In addition to intrinsic features (intrinsic signatures) of the printer, modulating the printing process to embed specific features (extrinsic signatures) will further extend the encoding capacity and decoding accuracy. One of the key issues with embedding extrinsic signatures is that the embedding should not degrade the image quality, but needs to be detectable by a detection algorithm. In this paper, we will demonstrate the feasibility of embedding code sequences in electrophotographic halftone images by modulating dot size through laser intensity modulation. We have developed corresponding embedding and detection algorithms to embed and extract information. Experimental results indicate that using a 600 dpi native resolution printer's default halftone algorithm, we can encode 5 bits of information in every 310 printer scan-lines or approximately every 0.5 inches.Index Terms-Electrophotographic (laser) printer, extrinsic signature embedding, halftoned images, laser intensity modulation, printer identification.

Geometric distortion signatures for printer identification

“…Since the geometric distortion is smoothly varying 3 in situations where the halftone frequencies corresponding to the two signatures under consideration are different, the coarser signatures can be interpolated to the finer sampled version, using the physical coordinates on the sheet of paper for suitably registering the signatures. We utilize this process in our comparison of signatures computed for halftones with disparate frequencies 4 .…”

“…For these applications, it is vital that the documents be secure in the sense that they are tamper-proof, not readily replicable, machine/human verifiable, etc. Various methods have therefore been developed (and others are under development) to address these security concerns [1][2][3][4][5]. In addition to these security techniques, forensic tools for the analysis of printed documents are also of significant interest because they can provide valuable information to law enforcement and intelligence agencies [6][7][8][9].…”

Printer and scanner forensics

“…In addition, synchronization of the signalling periods becomes difficult. The issue of synchronization can be solved by using Gold sequences and repeating each symbol multiple times within the image [29] .…”

Steganography in clustered-dot halftones using orientation modulation and modification of direct binary search

“…As to hide information in a monochrome clustered-dot halftone, there are three methods: 1) shifting the dot-clusters; 11 2) changing orientation of the dot-clusters; 12 and 3) varying the dot size of the dot-clusters. 13 This paper proposes a novel message-embedded halftoning based on orientation modulation and the modified direct binary search (DBS) framework. Without damaging the embedded data, the modified DBS framework is employed in the last step of the system, and it thus ensures that the resulting data-embedded halftones have optimal image quality from the viewpoint of the HVS.…”