Project Gutenberg offers over 42,000 free ebooks in the public domain. Search for images from these texts at the link above.
Project Gutenberg offers over 42,000 free ebooks: choose among free epub books, free kindle books, download them or read them online.
Specific to Health Sciences is the database of images from Patrick Lynch from Yale University which are licensed under a Creative Commons Attribution license.
If you are looking for images specific to Health Sciences the Gray’s Anatomy database of images in Wikimedia is a fantastic place to start. All of these images are now available in the public domain.