UILaunchImageSize
A string containing the width and height of the image.
Discussion
This string represents the size of the display for which the image is intended. You must specify the width and height with respect to the device in a portrait orientation. In other words, portrait and landscape images targeting the same device would have the same width and height.
The format of this string is {width, height} where width and height are the size of the image in points. For example, the string {320, 480} specifies an image that can be used on an iPhone 4 or iPhone 4S.
If you do not specify this key, the image size is assumed to be {320, 480}.