流水號浮水印鑲入個人化郵票自我驗證防偽功能之研究

Abstract

自1999 年澳洲郵政率先推出個人化郵票後，在全球各國郵政引起一陣結合數位印刷技術的個人化郵票旋風，不少民眾訂製個人化郵票為留存紀念或實際使用郵寄。隨著科技的進步，現代人雖越來越少使用傳統的寄信方式傳遞訊息，但依然不減集郵所帶來的益智怡情，且物以稀為貴，使得某些特別的紀念郵票價值更是不減反升，漸漸走向「加值產品」的角色。然而，不肖人士利用郵票的有價證券特性，偽造郵票的事件層出不窮，許多專家因此致力於郵票的防偽功能發展，但個人化郵票以數位輸出可變印紋的特性，卻容易被忽略，尚鮮少有人為此設計防偽機制。 因此本研究目的在於應用數位半色調加密技術，以網點位移方式組成加密微結構，並透過郵票結合數位印刷所形成之可變印紋，彰顯可自我驗證防僞功能，藉此向民眾宣導，整體不僅提高對郵票的收藏意願，更增加趣味性與教育性等獨特價值。運用程式自動計算數位半色調加密網點，嘗試將流水號浮水印加入不同色版，並藏入個人化郵票，使用柱狀透鏡解密後，與右下角外顯序號互相對應，即為自我驗證之防偽功能。 此研究結果曾於2015 年台北亞洲國際郵展實際進行設計輸出及推廣，成果顯示此方法是可行的，本研究所開發之防偽自我驗證功能穩定，且若使用影印機複印，因加密訊息區的網點細緻度高，隱藏訊息無法複製；亦或是遭人塗改其中一外顯流水號時，便可馬上辨識出郵票已經變造；且因程式可即時運算圖檔，可依輸出需求量印製此加密郵票，達到依需求可做彈性調整輸出列印，避免大量庫存。 最後，為延續以上研究成果，另外測試於整枚郵票中影像藏入流水號，以不影響影像辨識、美觀為原則，兼具設計概念，並可解出與外顯流水號相對應之號碼，且同樣具有自我驗證之防偽功能與郵票的有價證券特性。Having applied digital printing technology in personalized stamps, it became a trend throughout the world's postal authorities. Due to the pre-paid value of the stamps, there are cases where counterfeiters would imitate them and create fraudulent versions. Although many experts are devoted to anti-counterfeiting, the integration of digital watermark and variable data printing (VDP) for personalized stamps has not been used. Therefore, the purpose is not only to improve the value of personalized stamps, but also its security. The technique we use is dot shifting of digital halftoning to embed watermarks in personalized stamps. It combines the use of hidden and visible serial numbers which are located at both the center and bottom right. By using the lenticular lens, decoding the hidden serial number is possible and shows whether the two numbers are identical. Many replication techniques won’t reveal the concealed number as the microstructure of the halftone dots is prestigious in quality and that altering any serial number will show fraudulence. According to the previous successful results, it will not only embed the messages in a specific area, but also to the whole stamp. The image on the stamp can still be seen clearly and be used as a real stamp. In the meantime, the concealed serial numbers can be still decoded by the lenticular lens which will match the revealed ones.