Detecting a thrown object hitting a wall in front of the camera?

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Hi

Has anyone any ideas on how I would detect a thrown object hitting a wall in front of the camera - the object could originate from any angle so I'm racking my brains on how I would determine when the object impacted the wall.

For example, I have the camera a fixed distance perpendicular to a wall - if i throw a ball at the wall, I want to track it then determine the moment of impact against the wall.

Would I use the diameter of the ball? As the ball moved further from the camera, the perceived diameter would shrink - I could then take the calibrated diameter and camera distance and assume the ball had hit the wall.

Does that make sense, is it possible or is there a better way

Thanks