Pretend you have a robot with a light sensor that resembles a color video camera. You would like to program your robot so that it can determine whether there is a apple in front of it. If it can find an apple, it makes a sound. Well a good first step would be to get the robot to understand what an apple is. Imagine for a monent that you can talk to your robot, and that it can talk back.
Apples are apple-shaped.
Look for something that's apple-shaped. Well, sort-of round with a dimple at the top and a little stem. The apple might be upside-down or sideways. You must look for stems in all directions. Forget about stems.