After the Evasion has been played out, Tom reveals that Miss Watson (feeling guilty about having considered selling Jim down the river) freed him in her will. Tom expresses no guilt about the way he has withheld that knowledge and used Jim himself, but he does give Jim $40 "for being prisoner for us so patient." This Kemble illustration may be meant simply to represent those narrative facts, although the way the figures are posed and the caption also suggest the drawing is intended to evoke the larger end of the story of slavery, the Emancipation brought about by the Civil War. In the narrative Huck says that Jim was "pleased most to death" with Tom's $40 -- and this is the only illustration in which he is shown simply smiling.
The Barrett Collection, UVA PS1305 .A1 1885b