Two weeks to the day that Tumblr announced new guidelines against “adult content” –from full-on porn to “female-presenting nipples”–the hiding of naughty bits from public view begins today. It could take a while, though. Tumblr says the site contains “tens of billions of GIFs, videos and photos” that have to be checked by scanning software that even the company admits is error-prone. Being the recipient of a false positive “totally sucks,” states a new company blog post . (Tumblr declined to tell me how many visuals have been scanned so far, or how long completing the process could take.)

“First and foremost,” it states, “we are sorry that this has not been an easy transition and we know we can do a better job of explaining what we’re doing.”

Related: Tumblr’s NSFW castaways are flocking to these lifeboats as a ban looms

The hiding of verboten posts won’t happen all at once, says the company, as there’s quite a backlog of visuals uploaded over the past decade to scan. But any new uploads will get reviewed and ruled on instantly. “Your content will not be deleted,” the post emphasizes. All decisions can be appealed for evaluation by “a real, live human” it says. The company, a subsidiary of Verizon’s Oath, also promises to streamline the process soon, although it hasn’t yet said exactly how or when.

Speaking of real humans–some imagery of them in the buff will still be allowed, says Tumblr. This includes, “exposed female-presenting nipples in connection with breastfeeding, birth or after-birth moments, and health-related situations, such as post-mastectomy or gender confirmation surgery.” Tumblr will also give a pass to “nudity found in art, specifically sculptures and illustrations.” (Good news for the Renaissance.) But naked pictures aren’t allowed, no matter how arty. Still, writes the company, “Tumblr will always be a place to explore your identity.” Censoring won’t apply to written content like erotica.

The Tumblr app returned to Apple’s iOS App Store late last week, after it had been banned in November, apparently over child pornography that slipped through the site’s filters. Tumblr says that plans to remove adult content were underway before the app was banned.

Correction: An earlier version of this article attributed the blog post to Tumblr’s CEO.