These are resources for accessing public domain images, etc. You will want to read the fine print to ensure that any resource you choose is public domain.

1. http://www.loc.gov/
2. http://compfight.com/
3. http://www.openculture.com/2014/03/new-york-public-library-puts-20000-hi-res-maps-online.html
4. http://www.openculture.com/2013/12/british-library-puts-1000000-images-into-public-domain.html
5. http://dp.la/
6. http://photogrammar.yale.edu/
7. https://secure.flickr.com/photos/internetarchivebookimages
8. http://www.pdsounds.org/
9. http://publicdomain4u.com/