1. If you claim that all radishes are red, then a picture showing red radishes sure helps.
2. If you claim that people push boats to make them go quicker, then a picture of people beside a boat shows nothing.
In the first claim, you show an example of your claim. In the second you simply show a boat accompanied with people. To make a decent analogy, you would have a picture of people pushing the boat(And in turn making it go quicker). This is obviously impossible to do, unless you're really good at analyzing photos, as a still photo can't show movement.