Who is this man whose face appears randomly? Throughout Sayonara Zetsubou Sensei, there's a picture (not animated) of a bald man's face that appears randomly (often as a censor). Who is he and what is his relation to the show (or their creators)? Does he randomly appear in other Studio SHAFT shows?
He is the mangaka's assistant, Maeda-kun. 

From the TVTropes page Manga: Sayonara, Zetsubou-Sensei:


  Fan Disservice: Some fanservice scenes can be a little awkward when they're censored by the face of Maeda-kun, Koji Kumeta's assistant, who sometimes is even facepalming disapprovingly. Shame on you.