"I don't always run Call of Cthulhu, but when I do..."
This is what I think about.
Sure, everyone has their own iconic fantasy illo for D&D (often with the name Trampier, Otus, or Elmore attached), but so few people talk about what they picture when other RPGs come to mind. I first saw "Ward 13" in the 4th edition of CoC and I've never been able to shake it. For me, its appeal is that this is one of those pictures that begs the questions of the viewer, "What the holy hell is going on here and how did it come to BE?!" I found a few Call of Cthulhu illustrations over the years that have the same effect, but this is my first. And you never forget your first.