My litmus test is, "What Would Bill Watterson do?" If an artist takes a one-time commission to paint a Calvin & Hobbes frame on a nursery wall, great. If it's

My litmus test is, "What Would Bill Watterson do?" If an artist takes a one-time commission to paint a Calvin & Hobbes frame on a nursery wall, great. If it's on a million t-shirts or Hobbes is selling medical insurance, then that is something different. The former comes out of appreciation, the latter, pure exploitation.