I bought a digital camera: EOS Kiss X6i last year.
This camera has an interface for remote controller. On examination, I knew this plug is 2.5mm stereo mini plug and has very simple mechanism. So I connected the camera and Arduino.
This page provides me with useful information.
Arduino read Analog-Pin 1 (connecting with a light sensor input). If the value of Analog-Pin 1 exceeds a certain value, Arduino outputs Digital-Pin 2 (focus) and 3 (shutter).
I think that taking pictures continuously is to place excessive strain on camera, so I set 30 seconds of delay.
The light sensor can replace other sensors or triggers. For example, Ethernet shield can be connected. I enjoy the extension of my camera's release.