噴墨印表機加密與解碼技術的實現

陳禹勛(Yi Shun Chen)

指導教授 ： 江佩如

國立中正大學/工學院/機械工程學系/碩士(2013年)

摘要

本文主要研究如何藉由列印文件來追朔該份文件的印表機。印表機是現今經常使用的印刷工具之一，除了特定的噴墨印表機，如特殊墨水噴墨頭印表機或者使用特殊列印紙張等，否則列印出來的文件經常是可以被仿冒的，當文件遭到仿冒，即容易侵犯到開發者的權益，商品或產品容易被複製或仿冒，而特定的印表機利用固有的特性於列印過程中嵌入特定的記號，除了保護作者版權權益也可以驗證文件真實性。本研究使用可程式邏輯(complex programmable logic device,CPLD)晶片控制光學編碼器的訊號，使列印文件文字偏移，以達到隱藏訊號的目的，同時維持列印品質，使人眼無法感知文字產生的偏移，之後利用掃描器及影像處理的技術將所隱藏的訊號提取出來。本實驗所使用的噴墨印表機為600 dpi，一頁由8 pt亂數選取的英文字母，單行間距，39列文字所組成的文件，共可隱藏18 bits的碼，當水平位移量為2 像素(pixel)時，bits 錯誤率為2.0370%。列印的文件若經其他印表機或影印機複印，則bits 錯誤率將大幅提升，顯示本實驗所產生的文件具有不可複製性。本研究同時使用里德所羅門碼(Reed-Solomon algorithm,RS）來偵測錯誤碼，平均每30組錯9組的碼，經RS碼訂正後，可降低至2組。本研究的編碼技術一頁A4文件最多可隱藏45bit。

關鍵字

印表機

並列摘要

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 text only document by horizontally displacing an entire text line through signal modification from optical encoder of inkjet printers. We have developed corresponding embedding and detection algorithms to embed and extract information. Experimental results indicate that using a 600 dpi inkjet printer, we can encode at most 45 bits of information in one A4 size of page.

參考文獻

[1] Mauro Barni, Christine I. Podilchuk, Franco Bartolini and Edward J. Delp, “Watermark embedding: hiding a signal within a cover Image”, IEEE Communications,39, 102 (2001).

[2] R.-W. Wolfgang, C.-I. Podilchuk and E. J. Delp, “ Perceptual watermarks for digital images and video”, in Proceedings of the IEEE, pp. 1108–1126 (1999).

[3] C.-I. Podilchuk , E.-J. Delp, “ Digital watermarking: Algorithms and applications”, IEEE Signal Processing Magazine,18, 33 (2001).

[5] T. Hsu , J.-L. Wu, “Hidden digital watermarks in images”, IEEE Trans. Image Processing , pp. 58–68 (1999).

[6] C.-T. Hsu , J.-L. Wu, “Multiresolution watermarking for digital images”, IEEE on Circuits and Systems II: Analog and Digital Signal Processing, pp. 1097-1101(1998).