An image or a doujin where a character in a Ribbed Sweater plays a heavily pivotal role in the story or message.
BTW, The picture can't just be a woman in a ribbed sweater because those will be removed at the earliest convinience; the image must portray some kind of message to the reader about ribbed sweaters, or the sweater itself must have a role in the story. Be it implicit, or explicit, the message must be there.