How Do I Access The Camera From The Lock Screen In iOS 5?
This feature is exclusive to iOS 5 users. From the lock screen, double-tap the Home button. This will bring up iTunes controls as well as a camera icon next to the unlock slider. Click on the camera icon to take a photo.
Note: since the phone is locked, you will only be able to see the photo once you take it. You cannot share it or view the rest of your camera roll without first unlocking the device.