It isn't eye liner actually. It's insomnia showing. They state that in the show... Or at least the fansub I own.

aww i see tears... his black eyeliner turns me on!

There is something about this wallpaper that is very eye catching. And I'm not talking about just the eye itself. In a way, it reflects Gaara's personality. But anyways, great wallpaper! ^_~

Ok. This picture, the original lines I drew then colored it to no end on photoshop. Just wanted people to know that.