More than anything, it's covers that sell comic books. Well, unless it's The Beano, in which case it's whatever manner of Frisbee or dart gun those toy geniuses have managed to cook up and attach to to front win a plastic bag that sells it. In the world of mainstream superhero comics, however, it's totally a judging-a-book-by-its-cover scenario. It's how artists like Alex Ross can make a living in the industry seemingly solely off of drawing covers, how Darwyn Cooke caused a stir last month by simply doing some front artwork for a bunch of DC comics.
Think about it: when you go to the comic store, you're confronted with what's close to anarchy. Well, not quite, since - so long as you're at a half-decent comic book store - the titles will have some sort of order, alphabetical or by publisher or otherwise. Still, amidst all the hundreds of new books on the shelves, it's next to impossible to sift through them and find the stuff you like.
Which is why covers are so important. Ideally, they will jump off the shelves and attract the right person's attention - the sort of person who would probably enjoy the comic inside, for example (although given some of the contrasts between cover and interiors, often this is tantamount to marketing films in completely different genres).
Sometimes, though, comics leap off the racks for the entirely wrong reasons. Because they are offensive, salacious, or just plain stupid - there's racist imagery, uncomfortable sexuality, and double entendres aplenty across these fifteen comic covers you won't believe were allowed to exist...