i just have hi resolution image for one of the apps, i am just going to reuse them and i don't have any normal resolution image equivalents for that. what happens when i just have all high resolution images and put that up in a 3gs device with iOS say 4.x ?. will it render properly ?
My next question is about the apple guidelines for this, do you guys know is there any rule that if we are planning to support device which are non retina and we just have retina images, will they reject the app ?
Scaling down all your images with imaging software would have been faster than asking this question. Anyway HIG actualy says low res is mandatory, retina is optional, but ios is smart enough to scale the high-res images down if you don't provide low-res.
http://developer.apple.com/library/ios/#documentation/userexperience/conceptual/mobilehig/IconsImages/IconsImages.html1