Ask him to delete it

"Please, dude," you practically beg. "Delete that picture!"

"Not a chance," Mark cackles. "You need humiliating."

"Who are you even gonna send it to?"

"fucking everyone, dude!"

"Please don't! Delete, I'm begging you!"

"Alright, fine, I'll delete the picture...but people still need to see this. Do what I say or I don't delete it."

"Uggh," you say. "What do you want in exchange for deleting it?"

"I wanna see you talk like a baby, whenever we're not at school."