Good quiz. A few "greats" that you might consider adding: Leif Erikson (if you can find an image), David Livingstone, Francisco Pizarro, John Hanning Speke, Vitus Bering, Fabian von Bellinghausen, James Clarke Ross and my hero - Ernest Shackleton.
Thanks. I tried to find one for Leif Erikson, but there wasn't a good one on Wikipedia. The rest might be too obscure to be able to recognize a phot of.