The National Portrait Gallery was founded in 1856 to collect portraits of famous British men and women. More than fifty thousand images of the National Portrait Gallery's Collections are available for academic use. Low resolution images are available to copy and distribute via a Creative Commons licence and higher resolution ones via a more restrictive Academic Licence. Look at specific pictures' "Use this image" information.
1856 - present
Details for both the subject and painter are included with each portrait.
Creative Commons license - Image sizes are 800 pixels on the longest dimension at 72 dpi.
Academic license - Image sizes are 2400 pixels wide at 300 dpi.
Freely available data on internet.