On iPhone 6, you get an image that has a value of @ 2x On iPhone 5 and 5, you get an image of Retina 4 @ 2x.
Check out this sample image that I set here. 
Result in iPhone 5

Result in iPhone 6

but on iPhone 4 and iPhone 6 you get the same image. During this time, you need to code for different devices. Because the apple does not provide a document for him. by then, if I get something new, then I will post here.
Thanks!
source share