臺灣博碩士論文加值系統

資訊隱藏技術可以將重要資料隱藏在數位影像中，以進行秘密通信；然而敵人也可以將秘密訊息嵌入在掩護影像中，以遂行危害國家安全的不法行為。因此，時至今日，資訊隱藏偵測技術的研究比資訊隱藏技術的發展更為重要。
資訊隱藏技術中之像素差值藏密法(PVD)透過調整像素對間之差值以進行秘密訊息之嵌入，其不但藏密容量較最低位元取代藏密法(LSB)多，同時也能維持良好的影像品質。雖然PVD能避免被RS偵測技術所攻擊，但是其藏密影像之像素差值直方圖會呈現不正常之分佈，本論文即基於此藏密特徵，提出基於卡方統計之像素差值藏密法的偵測技術，以進行PVD之偵測。
本研究採取不同自由度之像素差值對進行實驗，以獲取在不同門檻值之偵測正確率。實驗結果顯示，在自由度為10至14時，偵測正確率(AC)均可達到 80%以上，且在自由度12時，偵測正確率的表現最佳(AC = 84.69%)。其顯示，本文所提出之卡方偵測技術可有效偵測PVD藏密影像，為一有效且實際之PVD藏密偵測工具。

Information hiding techniques can embed important data in digital images for secret communication. However, the enemy also can embed the secret message in the cover images to perform illegal behaviors which may damage the national security. Therefore, the study of steganalysis is more important than the development of steganography for the time being.
The Pixel-Value Differencing steganography (PVD) embeds the secret information in digital images by adjusting the difference of pixel value between the pixel pairs. The PVD can not only provide more hiding capacity than those provided by Least-Significant-Bit replacement methods but also maintain a good image quality. Although the PVD can avoid being detected by the RS steganalysis, the histogram of the pixel-value differences poses an abnormal distribution. Based on this hiding characteristic, this thesis proposes a PVD steganalysis based on Chi-Square statistics.
Different degrees of freedom were adopted in this study to be tested for obtaining various detection accuracies (ACs) under different setting of thresholds. Experimental results show that the detection accuracies are all above 80% when the degrees of freedom are set as 10 to 14 while the accuracy is the best (AC = 84.69%) when the degree of freedom is set as 12. It means that the proposed Chi-Square based method is an efficient and practical steganalytical tool for detection of PVD steganography.

誌謝 ii
摘要 iii
ABSTRACT iv
目錄 v
表目錄 vii
圖目錄 viii
1.緒論 1
1.1研究背景 1
1.2研究動機 3
1.3研究目的及方法 4
1.4論文架構 6
2.文獻探討 7
2.1資訊隱藏技術發展 7
2.2卡方偵測技術 10
2.3像素值差異藏密技術 14
2.3.1像素差值量化 14
2.3.2訊息嵌入 16
2.3.3訊息萃取 18
2.4效能評估 19
3.基於卡方統計之像素差值藏密偵測技術 21
3.1 PVD藏密特徵 21
3.2像素差值直方圖之卡方統計 24
3.3偵測流程 25
4.實驗結果與討論 26
4.1實驗環境 26
4.2不同自由度下之門檻值實驗 27
4.2.1自由度2至8實驗 28
4.2.2自由度10至14實驗 32
4.2.3自由度16至20實驗 35
4.3實驗討論 38
5.結論及未來研究方向 40
5.1結論 40
5.2未來研究方向 41
參考文獻 42
自傳 46

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