# A Self-Recovery Fragile Image Watermarking with Variable Watermark Capacity
## 4 Experimental Results and Comparison Analysis
### Performance of Tamper Detection and Self-Recovery
#### 4.2.3 Collage Attack  
Collage attack introduced in [36] is a special attack for the watermarking method based on block-independent. Figure 8 gives the tamper detection and recovery performance for collage attack.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Algorithm** & **FPR** & **FNR** & **PSNR (dB) of Recovered Image** \\ \hline [PERSON] et al. [13] & 0.09\% & 26.13\% & 25.90 \\ [PERSON] et al. [25] & 0.16\% & 3.25\% & 35.05 \\ The proposed method & 0.25\% & 0.44\% & 36.13 \\ \hline \hline \end{tabular}
\end{table}
Table 4: Performance comparisons for copy-move attack using Goldhill image.  
Figure 7: Tamper detection and recovery performance for copy-move attack: (**a**) Original Goldhill image; (**b**) watermarked Goldhill image; (**c**) attacked image; (**d**) tamper detection result using the method in [13]; (**e**) tamper detection result using the method in [25]; (**f**) tamper detection result of the proposed method; (**g**) image recovery result using the method in [13]; (**h**) image recovery result using the method in [25]; (**i**) image recovery result of the proposed method.  
A car from watermarked Car1 image (Figure 8a) is copied and inserted into watermarked Car2 image (Figure 8b) without changing its relative location. The detection results in Figure 8d-f indicate that the proposed method and [25] can resist the collage attack and locate the splicing area successfully. Only the border of the tampered area is detected in Figure 8d. The reason is that the method proposed in [13] does not break the block-independent characteristic during watermark generation and embedding processes. From the restored images shown in Figure 8g-i, it can be observed that both the proposed method and [25] can restore the tampered image with good subjective quality. The watermarking method in [13] cannot reconstruct the tampered regions due to the fact that the collage attack has been survived from the detection process. From Table 5, we can see the recovered images obtained by the proposed method and [25] have similar PSNR values. However, compared to [25], the FNR of the proposed method is much lower, which suggests a better tamper localization result.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Algorithm** & **FPR** & **FNR** & **PSNR (dB) of Recovered Image** \\ \hline [PERSON] et al. [13] & 0.14\% & 97.33\% & 24.76 \\ [PERSON] et al. [25] & 0.27\% & 0.14\% & 47.17 \\ The proposed method & 0.28\% & 0 & 47.79 \\ \hline \hline \end{tabular}
\end{table}
Table 5: Performance comparisons for collage attack using Car1 and Car2 images.  
Figure 8: Tamper detection and recovery performance for collage attack: (**a**) Watermarked Car1 image; (**b**) watermarked Car2 image; (**c**) attacked image; (**d**) tamper detection result using the method in [13]; (**e**) tamper detection result using the method in [25]; (**f**) tamper detection result of the proposed method; (**g**) image recovery result using the method in [13]; (**h**) image recovery result using the method in [25]; (**i**) image recovery result of the proposed method.