I discovered that the National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS) has launched a searchable Image Gallery. According to the site, “Images found here are in the public domain; however, we ask that you not use this material to promote or endorse commercial products or services. Please credit the source as: National Institute of Arthritis and Musculoskeletal and Skin Diseases (except where indicated otherwise)”
This collection complements the NIH Public Access Policy for federally taxpayer-funded research.
Bloggers and non-profit publications will also be enthusiastic users of some of these dramatic photographs in the public domain. There is an advanced search of this image collection where you search fields to find specific examples (unfortunately, it does not appear you can combine fields in a single search). The search fields include: