I assume that you are referring to the political cartoon that is in the "picturehistoryprints.com" link below. If so, the cartoon is saying that Harrison's presidency was very "little," very insignificant and inglorious, when compared with that of a giant like Abraham Lincoln. By contrasting the very small Harrison with the very large Lincoln, the cartoonist is saying that Lincoln is a "giant" of American history while Harrison is a tiny personage who has done little and has been plagued by scandal.
Most historians would argue that this is somewhat unfair to Harrison. Harrison was not a giant like Lincoln, but neither did he live in a time when there were major issues to be dealt with. The major issue of Harrison's time in office was a tariff -- not exactly the sort of thing that makes a president a "giant."