There are many great images on the Internet. But like any information you must credit the original source. Here are several web sites that offer a range of images you can freely use.
Public Health Image Library (PHIL)The Public Health Image Library offers a number of topical image collections on topics like influenza, bioterrorism, lab science, and more. Also of interest are image subsets selected for their interest to particular audiences: health care providers, teachers & trainers, librarians & researchers, students, consumers, and more.
NLM Digital CollectionsNLM’s Digital Collections allow searching and browsing numerous document collections: Images from the History of Medicine, World War 1, Medicine in the Americas 1610-1920, and many more. You can also search the collections for only images.
The Visible Human ProjectThe Visible Human Project created publicly available three-dimensional representations of a male and a female human body. These images include cross-sectional cryosections, CT, and MRI images.
MedPixMedPix is an open access online database of medical images, teaching cases, and clinical topics.
Includes over 1900 images along with text, tutorials, laboratory exercises, and examination items for self-assessment that demonstrate gross and microscopic pathological findings associated with human disease conditions.
National Cancer Institute: Visuals OnlineThe National Cancer Institute offers a collection of featured medical images in several collections: science & technology, childhood cancer, Spanish-language images and diagrams, anatomy, historical images, and B-roll videos. The full collection is also searchable.