The ability to design and deliver a presentation to an audience is one skill that we can teach our students that will have life-long application. For the past ten years, we have integrated Powerpoint (and now Keynote) presentations into our curriculum, giving our students valuable experience with this skill. I do not know, however, how much time we have devoted to the fundamentals of good slide design.
In this post, I would like to address one facet of good design, using images for the greatest impact. We have all seen presentations that were just massive blocks of text, usually bullet-pointed, that was then read to us. What presenters should be doing is telling a story, and sometimes that story is accentuated by an image.
Imagine a story being told about ancient Rome and the transition from Republic to Empire; to tell that story well, we would need to talk about Julius Caesar. (You can substitute any topic, figure, event, or issue that you want.)
This is the default slide that Powerpoint encourages. Notice the title, picture, and box of bullet points.

This slide could be fancied up by applying a template or some color, but that does not change the "design" of the slide.
The version below is slightly better in that it moved the dates of Caesar's life into the context of Caesar's image, and it has removed the block of text. The block of text should be spoken by the presenter and expanded upon. All too often though, that text is read to us, and then the slide is advanced to the next. The slide below is better because the audience will focus more on the presenter, and the presenter will have to talk about Julius Caesar crossing the Rubicon and all that entailed.

Notice how much more effective the above slide is, compared to the one below. A picture is far more engaging than clip-art, which should almost never be used.

Returning to the slide with Caesar's image, I think it would have greater impact if the limited text that we have on the slide now "popped" more; it needs to have greater contrast. For some reason, white text on a black background has greater impact.

It is looking good! There is still quite a bit of unnecessarily blank space on the slide. If a slide is going to have an image, then use the image to its fullest, as in the slide below.

As with all things, it is possible to go too far. The slide below, for example, has stretched the image too far, distorting its properties, and distending poor Caesar's face.

Below is the final version of the slide. I've added a citation for the image, since I did not take the photograph. Given even the barest of information as in this caption, one could search for "Andrew Hitchcock" 2006 "julius caesar" and find the image without any difficulty.

I think the slide above provides a good background for a presenter to talk around. They cannot read from the slide, but the audience is able to see a picture of Julius Caesar while hearing about him, and they have an important quotation that serves as a historical benchmark, as well as the most relevant year in terms of the story being told.
With a little more time to invest, I might consider making the strangely shaded background behind the photo of Caesar's bust transparent. That would put the bust, with its while marble, directly atop the stark black background for extra impact.