There are numerous pictures of Wilhelm Furtwängler available on the web but many are quite familiar and also repetitively seen. There are some commercial picture archives too, e.g. Getty images.
Here is one which is less often mentioned or referred to, and although it contains only 65 pictures, they are nevertheless not all familiar ones. It is well worth taking a look at them: https://www.sz-photo.de/result_webshop/wilhelm-furtwaengler/dossier-1.735248