| Oberman, Anthony |
| Oberteuffer, George |
| Ochtervelt, Jacob |
| Ochtman, Leonard |
| Ochtman, Mina Fonda |
| Oddie, Walter Mason |
| Odelmark, Frans Wilhelm |
| Odevaere, Joseph-Denis |
| Oehme, Ernst Ferdinand |
| Oehmichen, Hugo |
| Oertel, Johannes Simon |
| Ogilvie, Clinton |
| Olano, Ignacio Diaz |
| Olivie-Bon, Leon |
| Olivier, Ferdinand |
| Olrik, Ole Henrik |
| Ommeganck, Balthazar Paul |
| Onderdonk, Julian |
| Onderdonk, Robert Jenkins |
| ONeill, George Bernard |
| Opdenhoff, George Willem |
| Opie, John |
| Ord, Joseph Biays |
| Orrente, Pedro |
| Orsi, Lelio |
| Ortiz, Jose Benlliure |
| Ortolano, |
| Osborne, Walter Frederick |
| Osservanza, Master the |
| Osthaus, Edmond H |
| Ottesen, Otto Didrik |
| Ottinger, George M |
| Ottmann, Henri |
| Oudry, Jean-Baptiste |
| Ouless, Walter William |
| Outin, Pierre |
| Ouvrie, Pierre Justin |
| Ouwater, Isaak |
| Overbeck, Johann Friedrich |
| Oxford, William of |
| Our Original Collection |
| O'Neil, Henry Nelson |
| Ovens, Jurgen |
| Ollivier, Michel Barthelemy |
| Orcagna |
| Orchardson, Sir William Quiller |
| Oesterley, Carl August Heinrich Ferdinand |