in a work an artist has created. It is largely (and primarily) about retaining the rights to how one's work may be used.
Think of it this way: Say I'm a visual artist--should Ted Cruz be able to take my image and use it on one of his campaign flyers ? Should a crappy vodka company be able to lift it and use it for a bottle label? Should an "appropriation" artist such as Sherrie Levine or Richard Prince be able to use it in their work? Should a museum be able to reproduce it in one of their catalogues? The answer to the first two questions, in my case (your mileage may vary) would probably be no; the answer to the last two would probably be yes.
That is why artists subscribe to ARS (Artist's Rights Society) and VAGA, to field such requests. Sometimes (say, you're okay with the vodka bottle), a fee is charged; sometimes (say, for the museum catalogue) no fee is charged, according to the artist's wishes. The creative output of an artist is like their children: you can't just take their children without asking. The artist has a right to protect his or her reputation.
It's why the government passed the Visual Artists Rights Act (VARA) in 1990. http://en.wikipedia.org/wiki/Visual_Artists_Rights_Act
ON EDIT: the comic would not fall under VARA protection, since the law protects only "paintings, drawings, prints, sculptures, still photographic images produced for exhibition only, and existing in single copies or in limited editions of 200 or fewer copies, signed and numbered by the artist."