I would assume that the speed camera flashes pulses of IR light and measures the time taken for the light to return/ bounce back. Then by doing some maths you will be able to find out how fast a car is moving. Then that triggers the camera to take a photo, if no conventional flash is used, an IR Flash can be used also because cameras pick up a wider range of wavelengths than the human eye, including IR light. Use your phone camera and point it at the LED of a tv remote and press some buttons and you will see the LED flash.
I would assume the road markings are used to identify the camera that took the photo (note the number 744). Some cameras will use them to give a scale of distance, if two photos are taken with a known pause between them, by comparing how far the car has traveled in between the two photos you can confirm that the car was speeding.