One of the techniques that Carmen Taran mentioned in her Outstanding Presentations Workshop 2011 presentation, that can help you create more authentic slides, is to hand-sketch a diagram or image on a piece of paper, scan it, and add it as an image to a presentation.

Here’s an example:

Here are the steps:

1. Sketch something on a piece of paper.
2. Scan it to an image format.
3. Insert the image onto a slide (Insert>Picture).
4. Click the Format tab, then click Color in the Adjust group. Choose one of the settings that works for your slide. In this situation, I needed the color of the sketch’s paper to be different from the white background of the slide, so I chose an option that gave the picture’s background a yellowish tinge.
5. Add a shadow to give the effect of the paper being slightly off the slide. Choose Picture Effects> Shadow on the Format tab. (In 2003, choose Shadow from the Picture toolbar.) Choose one of the options. In 2007/2010, I suggest then choosing Picture Effects> Shadow again, then Shadow Options to open the Format Picture dialog box, with the Shadow category displayed. You can almost always play with the settings to get a more striking shadow effect.
6. If you want, add a pushpin. Choose Insert> Clip Art and search for pushpin. I used PowerPoint 2010’s Remove Background feature to eliminate the background.