From reading the CA3 notes, I get the impression that photos or clip art don't get you any marks and that a dull presentation without jokes or controversy is what's sought after. Therefore I can't understand why anyone would bother putting pictures in if there's no marks for it?
My short answer is... I can see what you mean! The slightly longer answer is that some graphics can help to meet your objective in communicating. An example is the see-saw graphic in slide 4 of our model solution to Assignment X1.2. This graphic is there as a communication tool - not simply a means of enlivening what might otherwise be a dull presentation!!