Fantasy Object on Fantasy Background (probably a sword on a wooden table or a map).
I fail to see the relevance to the story.
Randall Flagg is very clearly the devil himself and the story concerns his defeat, but I agree with Danny that there is no combat between two individuals and you would expect to read what you see at some point. On the other hand, I haven't read the Dark Tower series and if he appears in all the books then I expect that would explain itI expect they're personifications of good and evil
I think that is probably very true within the SF genre as a whole. There is a discussion somewhere on Chronicles about how iconic artwork for covers was re-used over time for several different books, with no resemblance to the stories in books that they covered. It was just "science fiction enough" to make a good cover. I don't think this makes it right. If I see a spaceship on the cover, I expect a spaceship to feature somewhere inside the book. If I see, as @Danny McG put it, "someone dressed like a Jedi, fighting what appears to be a villainous character from Teenage Mutant Ninja Turtles," on the cover then I also would expect this to happen, even in some symbolic manner.Whether it actually represents the contents of the book is neither here nor there (from a sales perspective).
I fail to see the relevance to the story.
Someone dressed like a Jedi is fighting what appears to be a villainous character from Teenage Mutant Ninja Turtles