I made a userscript that mimics the functionality I've seen on some other boards. It scrapes all of the images visible on the page (not counting blacklisted images), checks their alt-text for tags, and adds these tags (with the count of how many times they appear on the page) to the sidebar. The ? pulls up the wiki for that tag, the + adds it to your current search, - removes it, and just clicking on the tag searches for just that tag.

Check out the userscript here so you can see the actual code.

It's super-rudimentary, and I've been updating it whenever I think of a new fix.