In retrospect, the final solution is brilliant in theme compared to the original picture. Black and white - hah!
I REALLY like puzzles where the image itself is the puzzle -- thanks for this really original idea!
Using a google form so we can check our answers is a great touch
FWIW, I got direct GIS hits for all slices except Rome, but got there after a few followup searches. Not sure if that was intentional?
The final solution is a bit of a leap... try to find some way to hint at the leap within the puzzle. Example (more to illustrate the thought than as a practical example): Maybe the pictures could be of famous libraries in the countries
Personally, I'd give this one an orange or maybe even red