Unlike nearly every camera ever made, the iPhone takes a picture when the "shutter button" is released, not pressed.*
I've gotten some nice snapshots, but only after I figured out my current process:
- Press and hold the shutter button
- Compose the shot
- Release the button
*Yes, many digital cameras feature a "two-stage" process (half a press to focus, full to capture the image), but most take the photo upon a full press, not release, of the shutter button.