The point of adding images to a presentation is to show your views the picture or the message you trying to point a cross also make them understand your presentation better. When you find the right picture for your project it makes thing much easy and you get message going across faster views understand little bit more everything come out perfect with less stressing and the wrong just make everything blind it makes people thing that you don't know what you suppose to do then you get mad at yourself and end up with the project. 

i think the difference between animation and a transition in a presentation project is interesting because it shows you the complete difference between the same thing that are similar with the slides changing background.