Comic books have been an important media for almost a century, but not every comic book ever made has been unforgettable for the right reasons. There are plenty of books out there that introduced a new character or crossed a line in an innovative or creative way, but for every stellar example, there are thousands of terrible ones sitting in boxes somewhere collecting dust.
Not every book can be worthwhile, but there are some that take the cake as being unforgettable for all the wrong reasons. When it comes to bad books, it's not always about the artwork or the story - many times, it's all about the cover.
Comics book covers are what draw in a reader, and a comic book cover can often be the most memorable part of an entire book. When people think of Amazing Fantasy #15, they don't consider the stories inside, they mostly focus on that iconic front page depicting Spider-Man Swinging through New York clutching a bad guy.
Covers have a lasting impression on fans, which is why some of the worst covers Marvel has done are ones they wish everyone would forget.