NARUTO: Fuu no Sho - Sugao no Shinjitsu...!!

Team 7 finishes yet another unremarkable mission. After Kakashi leaves them for the day, Naruto suggests an S-rank assignment: finding out what Kakashi looks like under his mask. Sakura is uninterested until Sasuke states he wants to help. They are abruptly approached by a man named Sukea, a travelling photojournalist and former Anbu who offers to help them break into the Third Hokage's archives to check Kakashi's personnel record.

(Source: Naruto Wiki)