Hand drawn graphics can work great together with images in slides. As an example, see these ads below. (I am not sure whether these ads do a good job in selling markers, they are great though in warning you to take care of your health).



It is possible to draw shapes using a mouse or a drawing pad in PowerPoint, but I always find it hard to replicate that marker effect. Instead, I scan in real hand writing using a scanner, and then kill the white background with the Photoshop color range filter.