Just chiming in here to say that this is very much like security through obscurity. In this context the "secure" part is being sure that the images you host are ok.

Bad actors using social engineering to get the banlist is much easier than using open source AI and collectivly fixing the bugs when the trolls manage to evade it. Its not that easy to get around image filters like this, and having to do wierd things to the pictures to be able to pass the filter barrier could be work enough to keep most trolls from posting. Using a central instance that filters all images is also not good, because now the person operating the service is now responsible for a large chunk of your images, creating a single point of failure in the fediverse(and something that could be monetised to our detriment) Closed source can not be the answer either because if someone breaks the filter, the community cant fix it, only the developer can. So either the dev team is online 24/7 or its paid, making hosting a fediverse server dependent on someones closed source product.

I do think however that disabling image federation should be an option. Turning image federation off for some server for a limited time could be a very effective tool against these kinds of attacks!