In the older version of such as Confluence 4.3.7, the search result will show a preview in thumbnail form if it is a image as you can see from here

This feature is important for some user. Here's a good example of a scenario where this feature is important.

Imagine I want to search for the picture of a black cat. I search for "black cat" and probably get no results, because the pictures are not named blackcat.jpg but mycute_cat123.jpg etc. instead. So I try again and just search for "cat", now I get 50 results, great. But I have to click on all the attachments to find out, if it really is a picture of a black cat or not. Well, probably there isn't a black cat at all, so I spend minutes checking all the results for nothing. With thumbnails on the other hand, I could just quickly scan the thumbnail results and be done. So yes, the search might render 0.2 seconds faster without thumbnails, but what good is that, if the users task is nearly impossible to complete.

Due to this, I believe there should be an option for use to disable or enable this feature based on their need.

It would be good to extend this to files/attachments preview too.