In an update to the site's community guidelines, Tumblr now asks users not to upload any content that shows "real-life human genitals or female-presenting nipples — this includes content that is so photorealistic that it could be mistaken for featuring real-life humans," or "any content, including images, videos, GIFs, or illustrations, that depicts sex acts."
As part of this crackdown, Tumblr has employed an algorithm to spot and flag pornographic content.
"Filtering this type of content versus say, a political protest with nudity or the statue of David, is not simple at scale," Tumblr said. "We’re relying on automated tools to identify adult content and humans to help train and keep our systems in check. We know there will be mistakes, but we’ve done our best to create and enforce a policy that acknowledges the breadth of expression we see in the community."