1. Charles Darwin Portrait. National Portrait Gallery URL: http://www.npg.org.uk/
Common Creative License URL: http://creativecommons.org/licenses/by-nc-nd/3.0/
2. Louis Pasteur Portrait. National Portrait Gallery URL: http://www.npg.org.uk/
Common Creative License URL: http://creativecommons.org/licenses/by-nc-nd/3.0/
3. Antonie van Leeuwenhoek Portrait. National Portrait Gallery URL: http://www.npg.org.uk/
Common Creative License URL: http://creativecommons.org/licenses/by-nc-nd/3.0/