Harold Pierce Cazneaux (30 March 1878 – 19 June 1953), commonly referred to as H. P. Cazneaux, was an Australian photographer. In 1916, he was a founding member of The Sydney Camera Circle. He regularly participated in national and international exhibitions.

Cazneaux was born in Wellington, New Zealand on 30 March 1878. His father, Pierce Mott Cazneau, was an English-born photographer, and his mother, Emily Florence Cazneau, was a colourist, miniature painter and photographer from Sydney. Around 1890 the family moved to Adelaide, where the father began working for Hammer & Co., photographers with a studio in Rundle Street.

Cazneaux received further education at (unnamed) state schools in Adelaide, and worked for his father, taking night classes at the School of Design, Painting and Technical Art. In 1896, he started working for Hammer & Co. as a photo retoucher.

In 1904, Cazneaux moved to Sydney, where he took up a position with one of Sydney's oldest photo studios, Freeman & Co. He was later appointed the firm's manager and chief operator. At the same time he honed his photographic skills documenting the architecture of old Sydney, and in 1907, exhibited at the Photographic Society of New South Wales. In 1909, he held the first one-man photographic exhibition in Australia.

Cazneaux' prints were exhibited in solo shows in the windows of the Kodak Salon, Sydney, as well as international shows organised by the London Salon of Photography (1911 to 1952), and later included in the Royal Photographic Society of Great Britain's annual salons. In 1914 he won Kodak's "Happiest Moment" competition, ostensibly open to amateur and professional alike, and the £100 prize money went toward a deposit for his future home.

Cazneaux was a founder of The Sydney Camera Circle, whose pictorialist "manifesto" was drawn up and signed on 28 November 1916 by a group of six photographers: Cecil Bostock, James Stening, William Stewart White, Malcolm McKinnon and James Paton, later joined by Henri Mallard. This group pledged "to work and to advance pictorial photography and to show our own Australia in terms of sunlight rather than those of greyness and dismal shadows". He left Freeman & Co. in 1917 or 1918.

In 1921, Cazneaux was elected a member of the London Salon and in 1937 he was the first Australian to be conferred with Honorary Fellowship by the Royal Photographic Society. Beyond his photographic oeuvre, Cazneaux was also a prolific writer. As a correspondent for Photograms of the Year (UK) for more than twenty years, he was the international voice of Australian photography. He was official photographer for Sydney Ure Smith's lifestyle magazine The Home from 1920 to 1941, and was commissioned to produce images for a number of Ure Smith's publications, including Sydney Surfing (1929), The Bridge Book (1930), The Sydney Book (1931) and The Australian Native Bear Book (1932). He also contributed to Ure Smith's prestige magazines Art in Australia and Australia: National Journal. His work encompassed the whole range of realist photography: portraiture, street scenes and landscape, notably in later years the Flinders Ranges. He was fascinated by old and new Sydney, particularly the Sydney Harbour Bridge and beach culture. He was a master of bromoil techniques, blurring out distracting features. His daughters acted as assistants and often appeared in his images.

Cazneaux' work was championed for decades by the editor of The Home magazine, Sydney Ure Smith.