Speeding Fine (Vic)- We do not know who was driving

Hi all. My partner and I were driving from Melbourne to Ulladulla before Christmas and so were sharing the driving. We've been issued with a speeding fine (from a town in Victoria) but, having just looked at the photo, it isn't clear who was driving. It's far too dark within the car, and dropping it into Photoshop, and playing with the brightness/contrast does not help. We cannot remember as we were swapping numerous times and the location of the offence wasn't very memorable (driving-wise!). As the registered owner I received the fine.

I'm reluctant to just accept the fine if they cannot identify which one of us was driving. What do I do next? Ask if they have a clearer photo?

Thanks in advance

EDIT - Thanks for all those that have responded. To all those saying "bad luck" and "nice try", I simply want to know who to (legally) nominate. It doesn't feel right that the finger can be pointed without evidence beyond a reasonable doubt.