FVerbaas, I wonder if it is black/white, because some individual images are "CENSORED" (/s) and some entire blogs are shut down. So there must be some sort of deeper judgement going on.

Having the initial blocking done by a bot is rude and cold, yes. The task without a bot is impossible...there are millions of images on Tumblr. So, Tumblr provides a "WTF" button by which the blog owner can initiate a review, and humans get involved directly.

What would you suggest as an alternative? Full human review of every image on every Tumblr?