Whether you're working on a presentation or a portfolio, images play a crucial role in telling your story. That's not to say that you have to be a professional photographer and only use National Geographic worthy photos; your photos should reflect the story and experience you are trying to communicate. Sure, it's best to avoid blurry images, but if it captures the spirit of what you're trying to say, by all means, use it!
Often times using an image can mean you don't need to have a lot of text, which is a good thing because changes are people won't read it! Sometimes it will make more sense to show one image, while other scenarios may need multiple images (think photo storyboard) to get your idea across. Either way, visuals are a great way to grab the attention of your audience and keep them engaged.
"Did you know visuals are more deeply embedded in the brain than words?" The Science Behind the Magic of Visual Communication" [1:45 minutes]
Images and visuals also have the benefits of helping you remember the narrative and setting the pace for your talk. Rather than memorizing every word of your talk, let visuals help serve as a guide and a prompt for your key ideas. Visuals are also a great way simplify and clarify complex ideas.
Before turning to stock photography, consider which images you already have in your "image library" or can easily create through simple sketches and diagrams. Stock images (see Shutterstock, AdobeStock, etc.) are perfectly fine, but risk being a bit generic or too fancy (distracting) from what you really need. If you're using your own images, it means that they're likely new to your audience too, which will grab their attention.
Another good option for images is the Creative Commons. These images have special licenses which encourage use and sharing of images. Anyone can add CC licenses to their images (Flickr allows you to do this).
In addition to photography and sketching, consider tools like The Noun Project to integrate simple graphic icons to communicate your ideas.
Color is another simple tool for creating visual interest. Consider changing the color of the background of your slide or the footer of your slide can be a way to denote different sections, chapters or themes during your presentation. Alternatively, changing the color of your typography can achieve this too. Avoid being all the spectrums in the rainbow – two colors can go a long way.
You may find you develop a "formula" for the style for your presentations and slide decks, but while you're starting out, don't be afraid to experiment and try different ideas, formats and templates. Just try to be cohesive and consistent within each deck.