"Back it up" may be a popular command in hip-hop, but what does it actually look like when put into practice?
Here's how it's done: lay flat on your stomach and then pop your butt in their air (like you just don't care) and then snap a photo head-on or from the side.
The effect emphasizes the rotundness of the butt, positioning it over the back and juxtaposing it against it against the flatness of the position.
It's definitely not for belfie beginners. See 15 pros demonstrate how it's done in the slideshow above.