Here are some sources for free images that you can use for your website, presentation, art project or whatever.
- Antique illustrations from The British Library on Flickr
- Computer stock photos from WOC in Tech Chat
- Free stock photos from Unsplash
- Free stock photos from Pexels. They have some pretty nice HD wallpapers too.
- Photos by the US government at its agencies are public domain. This means that photos from NASA (including the lovely Project Apollo Archive), USA Gov, the National Archives and many more that I haven't thought of.
- Historical Photos from http://nos.twnsnd.co/
- A small selection of historical and antique stock photos from Historical Stock Photos
- Free stock photos from Pic Jumbo (slightly spammy)
- Agricultural photos from the US Agricultrual Research Service
- Free stock photos from Every Stock Photo (a little spammy)
- Free stock photos from Free Pixels (a little spammy)
- Public domain photos from http://www.public-domain-photos.com/ (more spammy)
There are also companies which will give you free photos or credits on your first sign-up or periodically: iStock, Adobe Stock (fotolia), Shutterstock and Creative Market. And both Google and Flickr will let you search for CC licensed photos.