運用於個人化郵票之圖像加密研究

Abstract

個人化郵票是一種數位印刷的應用，圖幅多分為兩部份，在有面額的部份是預先以平版印刷大量印製，而附籤的部份則可以放置個人設計或喜好之圖案，以數位印刷機作少量多樣化輸出。此種可參與郵票設計的方式，對於使用者或郵票收集者來說，是一個非常難得機會並將之運用於各類紀念與公益活動上。本研究主要以兩種不同的網點加密技術，應用於個人化郵票之圖案內，對個人化郵票而言可製作具有獨特性的加密防偽加值功能成品。其一是以網點偏移的數位浮水印加密技術，將特定的圖案藏入青色版中，並可利用特殊的光學解碼器顯現出浮水印圖案；另一加密技術則提出以網點變形的方式，依網點形成機制設計一特殊形狀網點，並以不同方向之形狀來表示0或1，並加密於洋紅色版中，於輸出圖像後以掃描器擷取影像且分色取出洋紅色版，利用影像處理偵測，即可辨識出原先藏入之資訊。本研究結合了數位浮水印加密技術及印刷品安全文件的防偽技術，並考慮印刷條件，使實體影像的印刷品能兼具數位浮水印及資料隱藏的功能，且有良好的解密效果。此網點形成的機制加密於個人化郵票之附籤中，藉由數位浮水印技術來加強防偽效果，可提高有價證券之附加價值及收藏性與趣味性，在未來對於無附籤的個人化郵票及高品質現場印列郵資券廣泛運用時，可利用此加密技術來保護郵資票品的真實性且可以追蹤票品寄遞過程的功能。

Personalized stamp is an application of digital printing. One part of the stamp with face-value is by lithography printing, and the other part is by digital printing. This is a greater opportunity for users and collectors to design their own postage stamp. Since the personalized stamp is printed at small amount and with many varieties, it can be used at commemorative and public activities. In this research, two encryption methods are applied to personalized stamp by modified digital halftoning techniques. First, a hidden figurative pattern is encrypted in cyan channel by halftone dot displacement, and the hidden information can be retrieved by an optical decoder. Secondly, dot deformation in magenta channel is used to encode data, and the data can be recognized by digital image processing. In this research, we combine digital watermarking with anti-counterfeiting techniques with the consideration of printing condition. It integrates digital watermarking and data hiding techniques in printing security document. By the formation of halftone dots, encrypted data is added in personalized stamp. It can not only to improve counterfeiting ability but also to enhance the value added features. In the future, the watermarked personalized stamps and high quality meter can be combined together and we can verify and track the watermarked postage stamp by machine readable techniques.