Notes for iOS app icons:
1. iTunesArtwork icon file should be in png format, but name it without the .png extension.
2. The standard bit depth for icons and images is 24 bits (8 bits each for red, green, and blue), plus an 8-bit alpha channel.
3. You do not need to constrain your palette to web-safe colors.
4. Do not use alpha transparency in app icons.
5. Higher resolutions versions should tend to be richer in texture, more detailed and more realistic.
6. Do not use rounded corners, drop shadow or reflective shine since iOS will add these effects automatically.
7. Use a visible background (something that will not disapear on the Home screen)
8. Note that the final visual size of a Spotlight search results icon on iPad is 48 x 48 pixels (96 x 96 pixels in high resolution).
iOS trims 1 pixel (or 2 pixels, for high resolution) from each side of your artwork and adds a drop shadow. Be sure to take this into account as you design your icon for Spotlight search results.
Also, we'd like the icon to not have a border, so that we can use the same icon for both iOS 6 and iOS 7. (For iOS 7, Apple has changed the corner radius, which means the borders will be off).