General feedback on Conway's Game of Life implementation
Separate different concerns in your code.  The function simulate does two things that should be separated, namely changing the state of the world and calling the function that saves it as an image.  As it is, it's impossible to re-use only the state-changing logic.  Instead, move the game logic to a function simulate_step (or whatever you want to call it).

Stick to the PEP8 naming conventions: functions and variables should be written lowercase_with_underscores. Otherwise, you follow the guide very nicely.