https://arstechnica.com/gaming/2018/12/tumblrs-porn-ban-is-going-about-as-badly-as-expected/

In the run up to its total ban on pornography, Tumblr is using "algorithms" to determine if current posts are pornographic at all.

For some reason, the blogging site hopes that people running porn blogs will, after the December 17th ban, continue to use the site, but restrict their postings to the non-pornographic. As such, it isn't just banning or closing blogs that are currently used for porn; instead, it's analyzing each image and marking those it deems to be pornographic as "explicit." The display of explicit content will be suppressed, leaving behind a wasteland of effectively empty porn blogs.