Until you unlock the screen and enter the camera app, the time to take a shot might have passed, and a new app is trying to remedy this. QuickShot HD Camera puts a simple icon or widget on your screen, which lets you take a high-res photo with just one tap, based on your phone's automatic setting. The app lets you set the resolution, and also gives you the option for the phone to briefly vibrate, so you know a shot has been taken and saved in the gallery.
While the app is $3 and often buggy, most such applications in their first version are wobbly, and the developers ask that you don't downgrade the app, but rather send your issues with each specific handset, so they can improve QuickShot. The devs also promise a widget, autofocus disabling and a built-in gallery to arrive pretty soon.
source: QuickShot HD Camera (Google Play)