Apple had this undocumented function for screenshotting back on iOS 3.1, and kind of let you use it while waiting for better frameworks in iOS 4.0

At some point they started rejecting your app automatically if they found the symbol for that function in your app. I didn’t want to leave my 3.1 users in the dust for no reason, so I did the same trick to obfuscate the symbol name before dynamically linking it in.

It worked right up until they stopped supporting iOS 3.1 completely.