A Format Fuhrer is akin to a Grammar Nazi.
On posters (motivational or otherwise), having the correct format is essential (picture surrounded by a box, with the Caption and Subcaption below).
Format Fuhrer enforces the law of correct format, and usually has a few words to say.
*sees picture without a box around the picture*
Format Fuhrer: Format fail, GTFO!
Creator: WTF it's fine!
Admin: He said GTFO, bitch!