The Revelation of Kakashi's True Face

is a manga-omake included with the Sha no Sho.

Summary
Naruto secretly meets with the ninken to ask them what Kakashi looks like beneath his mask. Pakkun is surprised by the secrecy, all of the ninken having seen it before and thus finding it unremarkable. Since Kakashi doesn't like to be photographed they have nothing to show Naruto, so they instead offer to describe Kakashi's face for him. Each provides wildly different descriptions until finally deciding that Pakkun's version is the most accurate. Elated, Naruto runs off to tell Sakura. After he leaves, Kakashi comes to see the ninken without his mask on. Seeing his face, they realise that the description they gave Naruto was completely wrong.

Trivia

 * This omake is the second of three omake about Kakashi's face.
 * As it turns out in the third omake, Kakashi's face resembles Pakkun's version the most, despite the ninken thinking it looks completely different.