Scientific stock photography library
The Science Photo Library is a for-profit organization that sells images. This particular site contains the photography from Dennis Kunkel, a microscopist, known for unique photography taken with light and electron microscopes.
There are 5,000 light microscopy and electron microscopy images of Algae, Arachnids, Archaea, Bacteria, Fungi, Insects, Invertebrates, Medical, Plants, Protozoa, Vertebrates, and Viruses. Every image is available for sale and a license fee is required for use.