The list below provides a starting point for sites that host images that are likely to be available for your use on school projects and to share online.  If you want to use an image that is not freely available for use, you can always link to the image rather than copying and pasting the actual image on your project.
You must still provide a citation!

General

• Wikimedia Commons
• Flickr
• Google Advanced Image Search
• Pixabay

Photography

• Pexels
• Unsplash
• Magdeleine
• Realistic shots
• Wellcome collection (Health related images)

Government images (be sure to read the Rights Advisory)

• USA Search
• Local Government Pictures
• Select Internet Images

Clipart

• Public Domain Vectors

Art

• Getty Museum Search Gateway
• National Gallery of Art
• MET Museu m Collection (filter for Show Only: Public Domain Artworks)
• Yale Art Gallery (be sure to check copyright status underneath image– okay to use if it says public domain)
• Old Book Illustrations

Science, Health and Fitness

• Focus Fitness
• Nasa Image Gallery
• USGS Photo COllection
• CDC Public Health Images
• Images from the History of Medicine (check Rights section for copyright info)