Our Buddha nature is like a light in a house. Even if you close all the doors and cover all the windows, some light still shines through to the outside. That’s how we know Buddha-nature is there.
This photo looks like a double exposure, but it was taken through the huge glass window that covers the front entrance of the Dharma Hall at Jogyesa during Winter time. The light shining off the massive gold Buddha is just enough to shine through the reflection of the tree and buildings, just like our Buddha-nature.