so say i have a background that is 640x960. before i make this the background for my app, do i have to make sure the device has a retina display and if its not set the background as an image that is 320x480? or can i just set it as the background without checking the device. also, i know that doing it without checking at least looks like it works, because i tried it and it compiled and looked fine, but what does apple reccomend and what is best practice? also (sorry), if i do need to check if it is an iphone 4, is using Code: if ([[UIScreen mainScreen] respondsToSelector:@selector(scale)] && [[UIScreen mainScreen] scale] == 2) an ok way to do this? or would this include ipad or something like that?