so far no he hasn't. all those pictures of him without the mask are (fan made)Has kakashi ever removed his mask in one of those episodes??
oho i remember now ^^He was in the hospital without a mask, but the bedsheets were covering his face and naruto wanted to pull them off. don't know which ep. My best guess is after he overused his MS in the save Gaara arc. An other time he reveiled there was another mask under his mask. And his ninjadogs have seen him without his mask, they're telling about his looks here:Don't continue if you don't want to know what he looks like !