Stock image sites with affordable pricing schemes (iStockPhoto is one of them) have transformed PowerPoint presentations. While using a stock image instead of clip art will always lead to a better chart, there are many poor (and cheesy) images out there. How to pick a good one? A slightly random, rambling list of suggestions (resembling the creative design process):
  • Start with the slide design. Brainstorm concepts. Write down chains of keywords. Think through what images could work. Only when you are happy with the short list of design ideas, start taking the limitations of PowerPoint or your design skills (i.e., making complicated 3D compositions) into account.
  • Iterate, go back and forth between image sources. While a stock photograpy site might be the final source of an image, use Google Images as well to get ideas by seeing what sort of images are returned based on key words. Use Flickr for "real images", especially locations (check the license). Stock image sites usually go for "touristic" photo compositions of landmarks and/or artificially smiling models.
  • Models are not real people. I hardly ever use images with faces from stock photography sites, they hardly ever look natural (with the exception of children). Search "team" on iStockphoto and you will see what I mean (here). Sometimes these images are even funny (the opposite of what you want them to be. Photographer takes model that usually does fashion shoots, puts on suit, puts on spectacles without lenses, and hey: we have a "business person pondering his vision as he looks towards the horizon"
  • Leverage advanced search. Add the word "isolated" in an iStockPhoto search to get images on a white background. Sort iStockPhoto images by "most downloaded" instead of "best match"
  • Crop. Consider that you can zoom into images and take just a small detail if you purchase a high enough resolution. The photographer's composition does not have to be yours.
  • Avoid "cheesyness". Be careful with using renderings or illustrations, often cheesy. Make the conceptual graph yourself, use stock images only for the components. Ready-made stock photography conceptual images (i.e., a few dollar bills with an arrow going up in the background) do not look good. There is a good list of cliches (where is that accent) on the Slide:ology blog.
  • Think of color. In iStockPhoto you can narrow down images by color range, especially important for large, page filling images. If no option, use a PowerPoint color overlay to take the color out the color all together and replace it with an overlay of one of the colors in your color scheme.
  • Look at many, many, many images until you find something that catches your attention. A small thumb nail is enough (and actually better than the full size image) to check whether an image evokes some emotion in you.
  • Less is more. Look for white space, or in fact, any empty space to add text if required.