The number of Baum's Oz books that I haven't read is in the minority -- but the base image from this card is from one of them. The caption makes it clear that the A-B-Sea Monster is benevolent, and that the Scarecrow crossed this river easily with its aid -- but the illustration belies the "easy" part as it's obvious that the Scarecrow is filled with trepidation both about his journey, and about the creature who seems to be aiding him. Perhaps he fears reaching the other side only to be gobbled up? It seems that similar fears are on the mind of the young bride in the vintage photo pinned to the card.
This card roughly corresponds with the six of cups in a tarot deck... emphasis on the "roughly."