# A False Negative Study of the Steganalysis Tool Stegdetect
## 4 Results
\begin{table}
\begin{tabular}{l l l l l l l} \hline
**Sensitivity** & **False Negative** & **Likely False** & **jphide(*)** & **jphide(**)** & **OTHER** \\
**Value** & & **Positive (Skipped)** & & & & **-ALG** \\ \hline
0.1 & 97.60\% & 2.40\% & 0.00\% & 0.00\% & 0.00\% & 0.00\% \\
0.3 & 97.60\% & 2.40\% & 0.00\% & 0.00\% & 0.00\% & 0.00\% \\
0.5 & 97.40\% & 2.40\% & 0.20\% & 0.00\% & 0.00\% & 0.00\% \\
0.7 & 96.20\% & 2.40\% & 1.40\% & 0.00\% & 0.00\% & 0.00\% \\
1.5 & 90.80\% & 2.40\% & 4.40\% & 2.00\% & 0.20\% & 0.20\% \\
3.4 & 87.20\% & 2.40\% & 3.40\% & 0.20\% & 6.40\% & 0.40\% \\
5.2 & 20.60\% & 2.40\% & 66.60\% & 3.40\% & 6.60\% & 0.40\% \\
7.3 & 12.60\% & 2.40\% & 20.20\% & 55.00\% & 9.40\% & 0.40\% \\
10.0 & 10.00\% & 2.40\% & 11.00\% & 66.20\% & 10.00\% & 0.40\% \\ \hline \end{tabular}
\end{table} 
Table 4: Results of 500 images from seam carve untouched images with different sensitivity values. Figure 4: Overall false negative rate seam-carving untouched images with different sensitivity values. Phase three of the experiment analysis 700 images from the Department of Computer and Engineering, university of Washington image database. Each image was embedded with a different generated bits of a message using jphide. During the analysis of the 700 stego-images, 3.71% resulted in error between 0.1 and 10.0 sensitivity which compared to the volume of the images involved is quite small. In the case of the error images, stegdetect could not analysis because of the following stated reason. 1. Bogus DQT index 6, 2. Invalid JPEG file structure: SOS before SOF, and the last 3. Quantization Table 0 \(\times\) 00 and 0 \(\times\) 01 was not defined. The error rate can be seen in Table 5 below. It wealth noting that all the images analysed were subject to frequency counts. In other words, the analysis of any detection (false negative or jphide) was added to find the highest detection ratio (i.e., a number of times a specific detection occur). After which they were quantified as shown in Table 5 below. Figure 5: Changes in the jphide rate with different sensitivities for seam carve untouched images. Figure 6: Changes in other algorithms detected with different sensitivities. The false negative result between 0.1 and 1.5 sensitivity was 78.29% which is a bit high, then when the sensitivity was change between 3.4 and 10.0 there was a sharp drop and a continuous decline until it reaches 17.71%. Moreover, comparing the false negative results of the previous seam-carving images (both manipulated and untouched images) we realised that with the previous experiment between 0.1 and 3.4 they had a significantly higher false negative ratio which was 80% to 98% before it had a sharp decline. Though the images from Washington University seem to have had a low false negative ratio compared to the seam-carving images, they all seem to have had a sharp decrease at some point, then when the sensitivity was set to 5.2 it maintained a slow but steady decrease as shown in Figure 7 below. The detection results of jphide (*, ***, ***) started between sensitivity values (0.3 and 1.5), then there was a significant increase in the detection between (3.4 and 10.0). The detection for jphide (*) was consistently increasing until 3.4-5.4 sensitivity when there was a height jump, meanwhile, between 7.3 and 10.0 sensitivity the detection for jphide (*) started to decrease and jphide (**) also had similar result like in the case of jphide (*) where it experience a stable increase then a slight decrease with 0.7 sensitivity before it started to increase in detection again between 1.5 and 10.0 sensitivity. Finally, jphide (***) maintain a continuous steady increase in detection between 0.5 and 5.2 then a height jump in the detection between 7.3 and 10.0 as shown in Figure 8 graph below.