A black joke [graphic].

"The Prince of Wales, Mrs. Fitzherbert (three quarter length figures), and Fox are seated at a rectangular table playing cards. Fox, who is full face, sits behind the table between the Prince (left) and his partner (right). He has taken three tricks, and holds one card above his head, about to play it, looking fixedly at Mrs. Fitzherbert. His other hand is under the table. His opponents hold two cards, and have taken no tricks. The profiles of the Prince and his partner are blank, except for the eyelashes of the concealed eye of each. Fox's features, especially his eyes, are marked and swarthy. Above his head, and between two pilasters which decorate the wall, is a picture of a fox running off with a goose, while a bystander lashes at him with a whip; in the background is a windmill."--British Museum online catalogue

The picture of a fox running off with a goose, while a bystander lashes at him with a whip amplifies the subject; the title is a reference to the song "Black Jack.".