The British gave us an ensign with a Union Jack in the canton (as they gave to every other colony), which eventually we defaced with a southern cross (minus the fifth star because the four stars correspond to the four compass points). This is our fourth flag (What can I say, we have a proud tradition of changing our flag :-p ).
You can read more about the flag here.
When shrunk to thumbnail size it's difficult to identify the flag as belonging to New Zealand. When furled it might be possible to misidentify it as well.