I've explained on several posts regarding the very fine passages through the fins.

If you are grasping this concept, then you'll realize that you cannot take photo of the surface of the radiator and expect to obtain any valuable data from it. The problem is between the fins.

Hold the radiator up to the sun and peer up between the fins and see if you can discern any debris that blocks the airflow. It will be immediately obvious if you can see straight though the fins or whether the fins are partially blocked due to fine debris (likely).

So, just forget the photo and perform the task as recommended and report back with your results.