Section 16(4)(b) in The Indian Post Office Rules, 1933
(b)in the case of the other side -(i)a gummed label not exceeding 2 inches (5cms) in length and ¾ (2cms) in width, completely adherent to the card and bearing the name and address of the sender of the card; and(ii)engravings, illustrations, drawings and photographs on very thin paper and completely adherent to the card.