IPhone 4 images Local vs Server?

So I have been doing some research on how to handle the different resolutions of iPhone screens. In the documention, found here: https://developer.apple.com/iphone/library/documentation/iPhone/Conceptual/iPhoneOSProgrammingGuide/SupportingResolutionIndependence/SupportingResolutionIndependence.html#//apple_ref/doc/uid/TP40007072-CH10

They say that using a naming convention and doubling your number of assets is how to do it. This is all well and good for local images,开发者_如何学C but Doesn't discuss how to get images from a server. Do I just need to query the device resolution before I pull the appropriate image from the server? Is it just that simple?

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iPhone 4 has twice as pixels as older devices. Your image has to have twice as pixels if you want the image to be crisp on iPhone 4. So, that's it, you test to see which device is there and pull the image on the proper resolution.