Desmond O'Neill (floruit 1960s). 1 portrait.
L.O.. 1 portrait.
Harry Lawrence Oakley (1882-1960). 23 portraits.
Octavius Oakley (1800-1867). 4 portraits.
Colin O'Brien (1940-). 1 portrait.
Humphrey Ocean (Humphrey Anthony Erdeswick Butler-Bowdon) (1951-). 9 portraits.
Paul O'Connell. 7 portraits.
James Arthur O'Connor (1792-1841). 1 portrait.
Francesca Odell. 3 portraits.
Odieuvre (floruit 1742-1748). 1 portrait.
Alexander O'Driscoll (floruit 1840-1844). 1 portrait.
Geo. E. Oertel. 1 portrait.
Ino I. Offord (floruit 1897). 1 portrait.
Chris Ofili (1968-). 1 portrait.
David Ogborne (died 1800 or 1801). 5 portraits.
John Ogborne (1755-1837). 18 portraits.
Perry Ogden (1961-). 2 portraits.
Thomas Ogle (floruit 1870s). 1 portrait.
Samuel Oglesby. 1 portrait.
Kane O'Hara (Floruit circa 1803). 1 portrait.
Nicholas Okes (floruit in London 1606-39). 2 portraits.
Samuel Okey (floruit 1765-1780). 7 portraits.
Dominic Old (1963-). 8 portraits.
Reverend Thomas Olive (circa 1748-1799). 1 portrait.
Archer James Oliver (1774-1842). 6 portraits.
Isaac Oliver (circa 1565-1617). 60 portraits.
John Oliver (1616-1701). 2 portraits.
Peter Oliver (circa 1594-1647). 14 portraits.
Sydney Haldane Olivier, 1st Baron Olivier (1859-1943). 3 portraits.
Herbert Olivier (1861-1952). 1 portrait.
Dominick Andrew Olivieri (floruit 1820-1833). 1 portrait.
Alan Olley. 5 portraits.
Sean O' Mordha. 1 portrait.
Henry Nelson O'Neil (1817-1880). 1 portrait.
George Bernard O'Neill (1828-1917). 1 portrait.
Mary O'Neill (died 1987). 1 portrait.
Terry O'Neill (1938-). 65 portraits.
The One Studio (floruit 1910s). 2 portraits.
F. Onwhyn (floruit mid 19th century). 3 portraits.
Ivan Opffer (1897-1980). 20 portraits.
John Opie (1761-1807). 113 portraits.
Julian Opie (1958-). 5 portraits.
Moritz Daniel Oppenheim (1800-1882). 1 portrait.
Joseph Oppenheimer (1876-1967). 1 portrait.
Orchard. 1 portrait.
Sir William Quiller Orchardson (1832-1910). 4 portraits.
Cuthbert Julian Orde (1888-1968). 1 portrait.
Bryan Organ (1935-). 15 portraits.
Joannes Orlandi (floruit 1601). 1 portrait.
Daniel Orme (1766-1837). 14 portraits.
Edward Orme (1775-1848). 14 portraits.
Sir William Orpen (1878-1931). 26 portraits.
Christopher John ('Chris') Orr (1943-). 1 portrait.
Carlo Orsi (floruit 1881-1896). 1 portrait.
E. Ortner. 1 portrait.
Malcolm Osborne (1880-1963). 4 portraits.
Walter Frederick Osborne (1859-1903). 1 portrait.
Alessandro Ossani (floruit 1857-1888). 3 portraits.
Tim O'Sullivan (1959-). 4 portraits.
Frederick Ottens (floruit 18th century). 1 portrait.
Leonardus Henricus van Otteren (floruit 1671-1713). 1 portrait.
F. Otto's School of Photography (floruit 1860s). 1 portrait.
P. Oudry (floruit 1578). 1 portrait.
Walter William Ouless (1848-1933). 12 portraits.
Sir William Ouseley (1767-1842). 3 portraits.
John Outrim (born 1810-floruit 1874). 2 portraits.
Horace Ové (1939-). 12 portraits.
Jeff Overs. 3 portraits.
Henry Overton (floruit 1712). 3 portraits.
John Overton (floruit 1665-1707). 7 portraits.
Philip Overton (circa 1680-1745). 10 portraits.
Mike Owen (1954-). 31 portraits.
William Owen (1769-1825). 52 portraits.
Chris Owens. 1 portrait.
The Oxford School of Photography & Colouring (floruit 1860s). 2 portraits.
David Jowett Greaves Oxtoby (1938-). 1 portrait.
