Ah, quite simple. The screen very briefly goes black with a white box over where the targets are. The gun detects if it's pointed over at that white box or not, and...there ya go. The opposite is a white background with black boxes.
It's why you can actually cheat on duck hunt by pointing the gun close to a light bulb and shooting it. It'll think it's pointed at the white box.
My Mother.....I miss her, tremendously
Life hasn't been the same since she passed away, she is my best friend, and my heart still aches to this day.
This photo was taken 2 years before I lost her to cancer.