Hi Mainey,
I doubt anyone has fiddled with the photo in the speeding notice. Sprung fair and square. As you say, the image shows your GPS on the dash (recent purchase).
Forget Google Earth for time frame accuracy (the images could be 12 months old).
I guess you are saying the GPS didn't warn you of the radar or speed limit. You did mention recently that it would be good if all cars came with a GPS. This might be an argument against such a move.
Never trust your GPS for radar locations or speed limits (or even roads). Our GPS often tells us we are over the limit near home. The speed limit changed over twelve months ago. Doing 55 in a 60 zone - you are over the speed limit!!
They aren't the be all and end all of devices. Very handy and quite valuable at times but have their limitations. Such as up to date software. Impossible to maintain for all regions all the time.