How to uncrush pngcrushed images from an iPhone app bundle
If you copy an application bundle from your iPhone, or from your iTunes library, you might notice that the PNG files are all apparently blank and/or corrupt. This is because they have been compressed by "pngcrush."
To uncrush, use the iOS SDK:
mkdir uncrushed /Developer/Platforms/iPhoneOS.platform/Developer/usr/bin/pngcrush -dir uncrushed -revert-iphone-optimizations -q *.png