Open database of medical images
Open-access medical images: 


MedPix (by keyword, organic system, pathology and diagnosis A-Z)
Radiopaedia (by keyword)
PEIR Radiology (by keyword, organ or anatomic region)
Ultrasound Cases (by keyword and organic system)
Open Access Biomedical Image Search Engine (Openi) (by keyword)
Wikimedia Commons (by keyword)
Google image search (using the filter "creative commons," "public domain" or "open access")
Google image search (using filters: black/white, noncommercial, photo)


More:


Gray's Anatomy
Dermatology Atlas