I am quite certain it's not possible. AFAIK, Red Laser doesn't actually take a "normal" picture but uses UIGetScreenImage()
(undocumented but nevertheless allowed for App Store apps) to make a screenshot of the live video feed. Since the OS does not play sound on this occasion, they are free to play their own sound.
Edit for clarification: As of OS 3.1, you are free to substitute the standard camera interface with your own controls. So you could place your own shutter button on the screen and play your own sound when the user taps it, but AFAIK there is now way to get rid of the OS's standard shutter sound.
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