證件盜用手法以肖像變造為最常見，其原因在於證件照片與證件資料難以進行比對。針對此一辨識之弱點，本研究透過點陣調色法(ordered dithering)製作特殊網點半色調肖像，建立證件照片與證件資料之絕對關連性，降低證件變造的可能性。研究過程當中，我們成功建立自動矩陣產生器，提高網點演算效率，避免人為製程易發生的錯誤；此外，為抵抗不同網點形狀產生的干擾紋路，本研究透過改變網點排列規則與網點擴張正規化，有效提升影像品質。最後，特殊網點半色調肖像，透過十倍數放大鏡得以即時辨識隱藏資訊，完整執行加密與解密之安全機制。

To verify the linkage between the photograph and the personal data on the security document is the weakest point of authentication process and that is the reason why the alternation of photograph accounts for the major cause of fraudulent use. In order to withstand this serious attack, the figurative halftone dots designed by ordered dithering are applied to the output of portrait on the secured documents. While an identity document containing figurative halftone dots, its anti-counterfeiting feature can withstand the illegal alteration of photograph. In this paper an automatic method to generate a threshold matrix is developed to enhance the efficiency of halftone dots generation. On the other hand, the image quality is further improved by adjusting dots distribution and dot gain correction.

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