MedPixA free online Medical Image Database with over 53,000 indexed and curated images, from over 13,000 patients from the National Library of Medicine. Content is peer-reviewed by an editorial panel.
NIH Image BankThe NIH sponsors a centralized image service for the dissemination of primarily scientific, biomedical, and disease related imagery. Images posted to the NIH Image Gallery are considered free-to-use with credit.
Wikimedia Commons is a media file repository making available public domain and freely-licensed educational media content (images, sound and video clips). It acts as a common repository for the various projects of the Wikimedia Foundation.