The passage this second picture of the mate illustrates reads: "When he was getting out cargo at a landing, I was always where I could see and hear. . . . I wished I could talk like that." One thing we see in the illustration that's not in the text is the crew of slaves who are actually doing the work, and in this picture they're clearly not as "happy" as in the previous one. This picture even evokes the familiar Anti-Slavery images of drivers dominating field slaves, and thus goes much further toward depicting slavery negatively than MT's words do.
The Barrett Collection, UVA PS1314_A1_1883c