Sometimes, I'll see an image on a book cover and I'll just know I've seen it somewhere else before, on another book. Then when I finally remember the title of the other book and dig up the cover image, I find that it's...not the same. Close, sure, but the two covers are far from identical twins. Let's call them fraternal twins instead.
I've collected a few of these fraternal twins here. Sometimes, like with the first two examples, the similarities lie not only with the cover images, but with the titles as well.
17 and Gone by Nova Ren Suma and Pretty Girl 13 by Liz Coley
Girl in the doorway seen from behind, hazy image, black border, number in the title...alas, completely different color schemes. But whenever I see one, I always think of the other!
In the After by Demitria Lunetta and After the Snow by S. D. Crockett
The perspective is different in the Crockett title, but other than that, these two look so similar to me. And it doesn't help that their titles are so similar too.