If you don't want to destroy the integrity of the case, then all you will be able to do will be to operate the "shutter" button. A small motor or solenoid could be mechanically adapted to to push the button down(a cam on a motor shaft for example). A motor would be better, since you wouldn't get a sudden mechanical movement, which could cause camera shake.
What sort of range do you need. Most devices operating in the ISM bands are only able to operate up to a maybe a 100 metres with the omni directional antenna often used. To keep the antenna small, 2.4Ghz is the most useful frequency. You can do better with a yagi or "cantenna" antenna. Check out the nrf2401 from Nordic, sparkfun have modules, and I believe there is a board for the arduino, and there will already be code around for it. You need one with an external antenna connector if you want to use anything more than a pcb antenna.
If you need to be able to control more than the "shutter", then you will need to get a camera module, these are available as OEM products, and connect via a serial link to a processor. These allow a bit more control of the camera functions.
You will need a pair of transceivers, obviously,
don't know if that helps,
cheers,
Richard
