Fair use.

I actually believe Shepard may have violated copyright in this case or at least his fair use argument is not valid. Fair use is broken down into "comment and criticism" and "parody" and this image does not seem to be in either of these categories. One may argue comment and criticism but that is primarily used for using a quote from a book with the author’s permission in order to review, comment, or criticizes the book. Granted the image itself has been commented on, but not as a way to review the original image. It also couldn't be parody unless it was a republican image that he twisted into a democratic support image. The images themselves are too close to be different, especially if you look at the bottom edge of the original and the edge created above the word hope. If he had gotten the image elsewhere he probably would have finished the area where the tie was instead of leaving a blue background where "hope" is. All in all, Shepards argument of fair use seems invalid when broken into its two major categories.