In many questions we're likely to post an image of what we're looking for. And there are often multiple visuals for the answer. Is there a way to search the questions via the thumbnails posted on the thread? A more visual approach like in Texample.
One thing one can do is to perform a Google image search for
site:tex.stackexchange.com <search term(s)>
I am using this sometimes to find possible duplicates, and, according to my experience, this turns out to work surprisingly well.
Actually, I sometimes wish that users asking questions could do that search themselves. If they end up not precisely finding what they are looking for, they have still a starting point and "references".
It seems to be true, though, that this search works best if you have already a solution to the problem in mind because then you can add the relevant key words to the search terms.
Note though that this may only be valuable in select instances where posters did use images. Some threads only post an image in the question, but the correct answers may have been simple enough to not post an image. Also, if you're looking for a specific issue, it's often better described in the post (with words) than in an image; the image might have been added, but without any visual indication of the issue.
In short, I doubt you'll find what you're looking for using a visual search, because the Q&A environment is not set up in that way.