I hope it is not a webcam else I do not se how you can do that with a arduiono, not enough memory to hold the pics and usb stack for cam communication. No if it is a canon cam you can load chdk on it en tirgger it with a ttl pulse to make a picture. If you want simple interval pictures do not use a arduino but only chdk. Of couse if it is a canon cam.

Do you knwo what of cam it is??

I don't think the arduino can interface with a webcam. It would need to run a USB bus natively. A few of the newer arduinos and teensy's can do this. not sure if a webcam would work.

There are some Arduino projects to get a camera onto it. check out this list of hackable cameras

I wouldn't use the arduino, I am always hesitant in saying it is not possible (because technically I believe we can accomplish anything) but the difficulties would be enormous using an arduino. An arduino just doesn't have the horse power for a USB camera. You can get affordable cameras and modify them with public lab filters and do it (you will need to attach a SD card to the arduino) but a USB webcam would be very tough.

Another option - use a Pi or Beagle bone for camera/image processing, the infragram webcam plugs right into their USB port and they run linux so you can process images on board. Attach an arduino to the Pi or beagle bone and use the arduino for real time communications to the ground.

if you are stuck on using an arduino, get a JPEG camera from adafruit and convert it with a filter.