How does the Google Calendar app determine which images to show me for the seasons? The Google Calendar app for Android has these illustrations for each month:





They fit my current location (northern Europe) very well, but if I was in the southern hemisphere (where the seasons are opposite from here) or the tropics, they would not fit. 

I'm guessing that these images may change based on the user's location. If that's the case (which I realize it may not be), then how does the app determine this? Is it based on the geolication of the Android device, or the country of the Google Account the user is using?
These are independent of the location. I live in India and see exactly the same images as you posted for those months in question. Very few parts of the country experience snow and definitely not where I live. Wiki on Calendar also didn't mention that these are location based and it appears universal. These images can't be disabled too

Only the holiday calendar is country specific