近年來，拜數位科技發展之賜，使我們進入了多媒體通信的資訊時代裡，在這個資訊時代中，許多服務提供者(service providers)也都希望利用數位化的方式藉由網路如數位廣播網路將數位化的內容(如影像、視訊、聲樂)帶給收視(聽)者。然而，由於數位內容本身具有易於複製的特性，因此，數位媒體很可能在網路傳輸過程中被攔截或被合法使用者作非法的複製或轉售，服務提供者之智慧財產權(intellectual property right)將因而失去保障，此將嚴重影響數位廣播系統的發展。本論文將針對此問題，研究發展數位廣播領域裡的一個重要新技術—數位浮水印技術，以輔助數位廣播之蓬勃發展。在本論文裡，將利用數位浮水印新技術以保護數位媒體之智慧擁有者及使用者之權益，使數位媒體內容可更安全地使用於數位廣播網路應用上。
我們提出了一些有效的新方法來保護數位多媒體的智產權保護與認證。本論文除了將視覺密碼技術(visual cryptography)應用於強健浮水印(robust watermarking)技術作為智產權保護之研究外，另我們提出一種易碎型浮水印(fragile watermarking)應用於衛星通信廣播網路上。
在強健行浮水印方面，我們以視覺密碼技術將浮水印轉換成公開浮水印及私密浮水印，而僅將公開浮水印隱藏於原始影像，至於私密浮水印則保留於智財權擁有者。因此，縱然於演算法公開的情況之下，駭客亦很難以統計方法或其他方法萃取浮水印。所以，我們的方法比傳統方法具有更高的安全性。
在易碎型浮水印方面，我們在視訊傳送端將浮水印資訊透過雜湊函數隱藏於MPEG2之視訊流(video stream)裡的移動向量(motion vector)上；而在偵測端(monitoring station)，則可判讀移動向量相關資料而解回浮水印資訊。因此，解讀浮水印資訊是否完整，可以即時判斷衛星視訊內容是否遭竄改或惡意干擾。我們的策略是若偵測出遭惡意竄改或干擾，則可採取進一步行動(如快速偵測出干擾源之位置)，以赫阻不法行為達到保護收視者之權益。
實驗結果顯示，我們所提出的視覺密碼的強健浮水印方法除具有更高安全性外，並且可抵抗多種主要信號如JPEG壓縮、切割(cropping)、模糊化(blurring)、銳利化(sharpening)等處理及攻擊；而易碎型浮水印則可即時偵測出數位媒體遭破壞或更改內容，因此，我們所提出的方法可應用於數位廣播系統，以保護服務提供者之智慧財產權及收視(聽)者之權益。

In recent years, we have entered the era of multimedia information due to the widespread development of important technique－digitalization. In this age, many service providers really hope that they can use networks, such as digital broadcasting system, to deliver the digital content (video, image, audio, etc.) to the viewers or listeners. However, the digital media is very easy to copy or resell illegally because of the digital content with the property of easy duplicating. This leads to intellectual property right’s (IPR) infringement of multimedia content and the serious obstruction of the development of digital broadcasting system. To solve these problems, we have developed new technologies, concentrating on the digital watermarking schemes, to support the development of digital broadcasting. Two major purposes of digital watermarking are to protect the intellectual property right of multimedia content from piracy for the service providers and to identify the authentication of multimedia content for users.
In this dissertation, we would propose some practical and effective methods for the protection of owner copyright and the user authentication of images and videos in digital broadcasting network. First, we focus on robust watermarking strategies using the schemes of visual cryptography to protect the intellectual property right of service provider. Then, a fragile watermarking, which can be applied to the interference detection in satellite communication network, is proposed for protecting the programs of digital broadcasting video.
In robust watermarking, a visual cryptography technique is proposed as a way of solving copyright protection problems for digital images. Our watermarking method employs a visual cryptography to separate the watermark into two parts, a public watermark and a secret watermark. For watermarking security, only the public watermark is inserted into the original image, while the owner holds the secret watermark. Without the secret watermark, it is almost impossible to extract the watermark even if the embedding algorithm is published.
In fragile watermarking, to provide the content authentication of video sequence, the watermark information is embedded into the video sequence of MPEG-2 streams by modifying the motion vector. In the monitoring end, the watermark can be extracted from the watermarked motion vector. Hence, the monitoring station can detect the authorized code from watermarked signals to authenticate the video contents. If the watermarked signal has no authorization information, the watermarking algorithm can easily detect the illegal use, and thus make a decision (such as detecting the location of interfered source) for prohibiting the illegal content to distribute in public broadcasting network.
Various experiments on the proposed robust watermarking method are presented to demonstrate the robustness to most common image processing operations such as JPEG compression, cropping, blurring and sharpening. The fragile watermarking method can detect the content modification and unauthorized use of multimedia. Consequently, our watermarking methods can provide both the protections of ownership copyright and consumer right in digital broadcasting system.

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