Some websites with freely available images:
NHS Photo Library - http://www.photolibrary.nhs.uk/
The NHS Photo Library is a comprehensive resource for the NHS and related social care organisations, providing access to cost-effective photography for use in their communication materials. Access to the library and use of the images is for NHS organisations and Public Health England, Department of Health and related Arm’s Length Bodies (ALBs) who hold an NHS or Department of Health email account.
MorgueFile - http://www.morguefile.com/
Free photo archive. The term "morgueFile" is popular in the newspaper business to describe the file that holds past issues flats. Although the term has been used by illustrators, comic book artist, designers and teachers as well. The purpose of this site is to provide free image reference material for use in all creative pursuits. This is the world wide web's morgueFile.
Health Education Assets Library (HEAL) - http://library.med.utah.edu/heal/
Collection of over 22,000 freely available digital items for health sciences education. From the University of Utah J. Willard Marriott Digital Library.
Anatomy of the Human Body by Henry Gray - http://www.bartleby.com/107/
The Bartleby.com edition of Gray’s Anatomy of the Human Body has over 1000 engravings from the classic 1918 publication.
Honmedia - http://www.hon.ch/HONmedia/
Nearly 7000 medical images and videos.
Creative commons search - http://search.creativecommons.org/
Public Domain Pictures - http://www.publicdomainpictures.net/
A repository for free public domain images. Download high quality HD photos or upload your own.
Wellcome Images – http://wellcomeimages.org/indexplus/page/Home.html
This collection contains historical images from the Wellcome Library collections. The Biomedical Collection holds over 40 000 high-quality images from the clinical and biomedical sciences. Selected from UK teaching hospitals and research institutions, it covers disease, surgery, general healthcare, sciences from genetics to neuroscience including the full range of imaging techniques. Contains some images available free under CC licenses and some available to purchase.
Public Health Image Library – http://phil.cdc.gov/Phil/home.asp
Images and videos from the Centers for Disease Control and Prevention. Most of the images and videos can be freely used; for some there is a charge. The content is organized into hierarchical categories of people, places, and science, and is presented as single images, image sets, and multimedia files.
Google Images Advanced search - you can filter out copyrighted material:
Go to Google Images
Select Settings (bottom right of screen)>Advanced Search >Usage rights
Choose: ‘Free to use, share or modify, even commercially’)
You then search for images which are OK to re-use and modify.