Does the G10 have a remote release socket or IR remote?
My G9 doesn't, so that leaves just USB, or a DIY mechanical shutter-presser.
Or you could use chdk.
When I search for this remote it comes up with suggestions to use it with the G10. At least camera actually does have this 2.5mm plug (as well as a 3.5 plug for AV)
With a Canon SLR and remote release port, if you short the ground pin to one of the other pins it will either fire the camera or engage the auto focus. I wrapped wires around the ground and shutter pins, then soldered a switch to the wires. When you turn the switch on it will automatically take photos until your turn the switch off.
Use your multimeter and test the port! It likely operates in the same way.
the circuit will work for you, Canon uses that standard 2.5mm for most of it's hardwired releases. The software I wrote was for doing HDR, but I'm sure it's simple enough to modify for your own needs.
There's plenty of other folks that have done this, it's an easy project with a really nice payout- high speed triggers are very useful. My only recommendation is that you do use a circuit which uses an optoisolator, because some prototype circuits don't. Once you have the simple circuit to control the shutter release, the Arduino can use sensors of all kinds to "decide" when to release that shutter, and if you desire, for how long. Since the control code is so simple (just high/low on a pin), it's a GREAT one to do, with no more complexity than BLINK, in reality. Fact is, the isolator (inside) really is just an LED on one side, and a light-controlled switch (darlington phototransistor) on the other. To release your shutter, all you do is Blink, so to speak ;)
The isolator, which costs under a buck, will help save your camera from being destroyed if you make some type of error and feed power back into the camera. Have fun, and be careful. The project is pretty low-risk actually in terms of possibly damaging hardware, but it's good practice and all that. Be very sure to use isolation if you plan to use Flash or strobes in any way, especially external flashes of any sort. Hundreds and thousands of volts trigger those tubes, you don't want to backfeed that back into Arduino or your computer... and you'd be surprised how badly insulated/isolated most flashes are. My own prototype also controlled a flash unit, which had an internal short that I wasn't aware of.
That could have cost me my Canon EOS, or my computer- items I can't easily replace. Instead it cost me a fifty cent isolator. Lesson learned.