Gallery of the Masters 
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- O'Brien Lucius Richard
- O'Connor James Arthur
- O'Connor Roderic
- O'Kelly Aloysius
- O'Meara Frank
- O'Neill Henry Nelson
- Óbidos Josefa de
- Ochtervelt Jacob
- Oleszkiewicz Józef
- Oliveira João Marques de
- Oliver Isaac
- Opie John
- Orchardson William Quiller
- Orłowski Aleksander
- Orozco José Clemente
- Orpen Sir William Newenham Montague
- Orrente Pedro
- Osborne Walter Frederick
- Osborne William
- Ostade Adriaen Jansz van
- Ostade Isaac
- Oudry Jean Baptiste