Have use tried the new feature use camera on Lock screen in iOS 5 iPhone, with this new feature you can access the camera so easily from the lock screen, so no need to unlock the screen first and then the camera. Just Click the camera icon directly from the lock screen and start clicking the images.
Its simple and easy to use this trick on your iPhone iOS 5, First you have to update your device with new iOS, you grab the iOS 5 files from here.
How to Use Camera on Lockscreen (iOS) iPhone:-
After the iOS 5 Update you can enjoy this feature on your iPhone 4.
Double-tap on the Home button, a camera icon will appear next to the unlock slider
Tap on the camera for immediate camera access