You are looking to disable the camera?
There is no app that can do that because security restrictions don't let apps touch other apps and certainly can't disable hardware. (ironically because disabling the camera is probably for security purposes.)
Your best bets would likely be finding a model without a camera, don't know if they exist though.
Tape over the camera. (one of my dads previous employers required the IR port of his palm be covered with silver tape.)
Take apart the phone and physically disable the camera, which risks bricking the device.
I remember an old handspring/palm treo coming in camera and non-camera models.