I've made a somewhat experimental image search of all images on Danbooru available here:
Unlike the search engines built into Danbooru, this allows you to search with an image file to find if this or similar images have been posted here. It's useful for example to find the original when all you have is a defaced and artefacted aeriesdies version, without having to guess all the tags that might be on the picture.
Since I don't have a copy of the danbooru database, I have to do an md5 search for the post. This will come up empty if the image is marked explicit and you don't have a privileged account, in case you're wondering why the search engine finds a pic but danbooru claims to not have it.
At the moment it'll only find images that are at least a few weeks old since that was when I got the thumbnail dump. If the search is found useful I'll add a regular update for the latest pics so those can be found too.
Updated by piespy