Whether you are doing a public presentation or a popular science article, you are highly likely to include some sort of visual element. It quickly and efficiently establishes a shared understanding in the audience that you can then use to build your explanations on.
Different visuals serve different purposes. An animation might work better in an article and a photo might work better during a talk. It is up to you which to include to create the best flow not only in your story line but also in the understanding process of your audience.
Photos are easy to use and readily available online or from your own collection (documentation from the lab or field trips and so on). When you use photos in slide shows make sure the resolution is high enough to be shown on a projector. Also be sure to have the copyright in place. Some photos (even free stock photos) might have a requirement of crediting the owner.
Illustrations are nice to use as they can be tailored to the exact element, you want to show. As with photos illustrations that are available without costs might have a credit requirement associated with them, so be sure to check this before using the illustration. Also be aware to have a high resolution (e.g. use vector graphics).
If you choose to create the illustrations yourself, use an authorized program or online web tool. You can also contact a professional illustrator to create the illustrations exactly as you want them.
Animations are good to use to illustrate a certain process. The animation should be clear and intuitive, and can also serve as attention point for online readers who scroll through the article before reading it. If used during a talk you can talk over the animation and create a nice interplay between you and the animation.
Programming tools like Python can also be used to create animations, if you are a programmer.
Videos can be used much the same way as animations to show a certain process. It should not be used during a talk as a substitute for the talk. If you want to refer to an video recorded interview, you should rather refer to the interview and provide the link afterwards.