Nov. 28, 2012  -- Look again at that photo. Yes, we know, the first thing you think you see is a breast or a nipple. But look again. It's very clearly an elbow.

You looked closely. Facebook, however, didn't.

Last week a website called "Theories of The Deep Understandings of Things" came across the photo and decided to test Facebook.

"We post lots of art and also funny stuff on our Facebook page. Some of them, naturally, have some skin -- art and the non-art. We have discovered that Facebook standards are pretty much Bible-esque," the CEO of "Theories of The Deep Understandings of Things" told ABC News. He said he preferred not to reveal his name.

But this was a good way to test Facebook system, he thought. Last week he posted the photo that goes with this story. Facebook, as he expected, removed the photo.

"If we post a Renaissance painting consisting of a lady with, God forbid, a nipple, they'll remove it and block our personal account," he said via instant message. "We thought it would be a good idea to check on their standards, to make people ask themselves what exactly it is that is bothering them so much."

Yesterday, Facebook lifted the ban. "This photo does not violate our content standards and we have already restored the photo. We made a mistake removing the picture and apologized to the page admin," Facebook said in a statement. (ABC News could not track down the original owner of the photo.)

Facebook clarified to ABC News that it removes all exposed breasts from Facebook. Photos of breastfeeding women are allowed, just as long as nipples are obscured. Real-world works of art, however, including paintings, are permitted and shouldn't be removed.

Facebook, as we have reported before, has a User Operations Team -- a real team of humans -- monitoring photos and content on the site. It's not done by a computer. Last year, the site removed a photo of a child with Down Syndrome by mistake and provided more information on what happens when you click the "report" button.

But all that doesn't seem to impress the CEO of the site. "It's nice to know that tons of media-exposure can actually make FB be a little more sensible, or maybe a little more worried," he wrote on its Facebook page. "We can't wait for the next FB alertness test."

We hope Facebook is looking closely.