If adding photos to a presentation they are most likely “royalty-free” photos. The term is used a lot, so here is a quick overview of what it really means.
Royalty free photographs are offered for a one-time fee. When you purchase a rolyalty free image you can use the image as many times as you want, in as many projects as you want. As opposed to a fee for a specified number of times the photo is permitted to be used (which was the dominant business model 10+ years ago).
Royalty free also means the image is purchased for use in a product, not for resale as a stock image or as an image alone. Every royalty free company has slightly different guidelines, so be sure to review before use. The last tip is to check the image size (although with PowerPoint/multimedia this is not as critical as print design).
– Troy @ TLC