StockSnap is a royalty free stock photography site that is worth bookmarking for presentation design.
All images on the website are FREE and do not require attribution, both great things for presentation designers to hear! Photographers choose to share their work with StockSnap and release them under Creative Commons, so they can be used for personal and commercial use. There is a variety of imagery, with categories from business to nature. 
Select an image and all the vital information regarding the photo is available; photographer, dimensions, size and relevant tags.
When searching images, the site will advertise some images with watermarks. These, and “sponsored images,” are from outside websites that are not included in the free StockSnap library. If your project needs a good, free, image resource, this is a perfect option to have available.
Troy @ TLC