First, we consider the number of tasks that reach some specific degrees of satisfaction against varying degrees of satisfaction. The comparison is shown in Fig. 15. The horizontal axis represents the maximum degree of satisfaction through five operations. The vertical axis represents the number of tasks, whose degrees of satisfaction exceed some specific degree of satisfaction. Fig. 15(a) considers three typical DoS thresholds, and Fig. 15(b) shows more DoS thresholds. From the performance comparison in Fig. 15(a), our system performs better than those of Engines A and B. We can also observe that 75% of the tasks achieve the 10 satisfactory images in the top 20 images, which shows that our system is very powerful and that it indeed helps users to find desired images.