Noticed camera flash

I was driving and noticed a camera flash. I realized that I was photographed for speeding, although I knew that the speed did not exceed. Just to make sure of my assumption, I went around the block, drove again in the same place, and at an even lower speed. But the camera flashed again. I thought it was funny, and I drove past the camera three times the minimum speed, smiling into the camera, which is flipped every time I drove past. Two weeks later I received five receipts for driving with a non-fastened seat belt by the post ...