Thomas Annan (1829–1887) was a Scottish photographer, notable for being the first to record the bad housing conditions of the poor. Born in Dairsie, Fife he was one of seven children of John Annan, a flax spinner.
After his initial apprenticeship as a lithographic writer and engraver at the Fife Herald in Cupar, he moved to Glasgow in 1849 and worked as a lithographer and engraver for Joseph Swan until 1855. He set up business with George Berwick at 40 Woodlands Road, Glasgow, listing in the 1855 - 56 Glasgow post office directory as calotypists, practitioners of this early form of photography. In 1855, he photographed the ship RMS Persia, under construction on the Clyde, which was probably a commission by engineer, Robert Napier. This photograph was part of a group of images sent to the Photographic Exhibition in connection with the British Association.
After dissolving his previous partnership, he established himself in a photographic studio at 116 Sauchiehall Street during 1857. In 1859, the business moved to 200 Hope Street  and he was also able to establish a printing works in Hamilton in 1863. First interested largely in architectural photography and then portraits, as well as photographing artworks and maps, in 1866 Annan photographed slum areas of the city. These images were used by Glasgow City Improvement Trust to document the overcrowded, unhygienic conditions ahead of extensive redevelopments. It was this series of photographs, created between 1868 and 1871, entitled Old Closes and Streets of Glasgow, that ensured his posperity.
In 1869, Annan purchased the contents of Rock House, which belonged David Octavius Hill, which included many of Hill's photographs and negatives. These were eventually exhibited by Thomas' son, James Craig Annan, and reproduced in photogravure in Alfred Stieglitz's journal Camera Work.
His works include:
- Bond and free: five sketches illustrative of slavery. by J Noel Paton, photographed by Thomas Annan (1863)
- Portrait of David Livingstone (1864)
- Photographs of Glasgow College (1866)
- The Painted Windows of Glasgow Cathedral: A series of forty three photographs (1867)
- Photographs of Glasgow with descriptive letterpress (1868)
- Days at the coast, or the firth of Clyde, its watering places, scenery, and associations. (1868)
- Illustrated catalogue of the exhibition of photographs in the new galleries of art, Corporation building, Sauchiehall Street, photographed by Thomas Annan (1868)
- Three Old Maps of Glasgow, photographed by Annan. 1. Glasgow in 1777 by McArthur 2.Glasgow in 1807 by Fleming 3. Map of the Environs of Scotland in 1795 by Richardson (1871)
- Glasgow improvements act 1868: photographs of streets, closes & c. Taken 1868 - 71 (1872)
- Scottish landscape: The works of Horatio McCulloch, with a sketch of his life by Alexander Fraser. Photographed by Thomas Annan (1872)
- Historical notices of the United Presbyterian congregations in Glasgow by John Logan Aikman with photographs by Thomas Annan (1874)
- Photographic views of Loch Katrine, and some of the principal works constructed for introducing the water of Loch Katrine to the city of Glasgow (1877)
- The old country houses of the old Glasgow gentry. One hundred photographs by Annan with descriptive notices of the houses and families by John Buchanan (1878)
- Photographs of old closes, streets, & c. Taken 1868 - 77. Glasgow City Improvement Trust (1878)
- The Castles and Mansions of Ayrshire, illustrated in seventy views, with historical and descriptive accounts by AH Millar (1885)
After his death in 1887, the firm continued to produce volumes of photography, including the third photogravure edition of Old Closes and Streets, in 1900.
- The Castles and Mansions of Renfrewshire and Buteshire, illustrated in sixty-five views, with historical and descriptive accounts by AH Millar (1889)
- University of Glasgow Old and New, edited by William Stewart, illustrated with views and portraits in photogravure by Thomas Annan (1891)
- Photographs of Glasgow Harbour and Docks, taken 1892 - 1898
- The old closes and streets of Glasgow, engraved by Annan from photographs taken for the city of Glasgow improvement trust, with an introduction by William Young (1900)
Annan's photographs of the Loch Katrine Waterworks were praised in the British Journal of Photography: "The views by Mr. Annan could scarcely fail to be attractive, for in a country so beautiful a clever artist is bound to produce results in keeping with the nature of the subject, and this Mr. Annan has done." Indeed, Annan's work was often praised not only for its aesthetics, but also for its technical virtuosity. Twenty years later, Annan's studio would be singled out by Baden Pritchard for its accomplishments in carbon printing and "beautiful pictures of exteriors and interiors of Scotch strongholds."
Thomas Annan purchased the rights to the photogravure process in Britain from Karel Klíč of Vienna in 1883 after visiting the city with his second son, James Craig Annan. James was a noted photogravurist and associated with late nineteenth-century art photography continued in his father's profession, receiving a Royal Warrant as 'Photographers and Photographic Engravers to Her Majesty in Glasgow'.
Thomas Annan died on 14 December 1887 at his home in Lenzie. Before his death by suicide, he had experienced a month-long period of "mental aberration". 
The family business survives to the present day in the form of the Annan Fine Art Gallery, located on Woodlands Road in the West End of Glasgow.
A selection of prints from the Glasgow Improvements act 1868 series were displayed in the Scottish National Portrait Gallery from 2011 to 2012. In 2017, the Getty Museum curated an exhibition entitled Thomas Annan: Photographer of Glasgow, the first to survey his career and legacy as photographer and printer.
- Richard Howells, Review of The Other Half Revisited: The Legacy of Jacob A. Riis, The American Historical Review, 3 (1998), p. 1016
- Stevenson, Sara (1990). Thomas Annan, 1829-1887. Edinburgh: National Galleries of Scotland. p. 4.
- "The Post-Office annual Glasgow directory 1855 - 56, page 522". www.archive.org. Retrieved 27 April 2016.
- Glasgow Photographic Association Papers. Mitchell Library: MS 250 http://www.glasgowlife.org.uk/libraries/the-mitchell-library/pages/home.aspx
- "The Post-Office annual Glasgow directory, 1957 - 58 page 57". www.archive.org. Retrieved 27 April 2016.
- "The Post-Office annual Glasgow directory 1859 - 60, page 59". www.archive.org. Retrieved 27 April 2016.
- "Thomas Annan Collection - libcat.csglasgow.org". libcat.csglasgow.org. Retrieved 27 April 2016.
- Hannavy, John (2008). Encyclopedia of Nineteenth-Century Photography. Routledge. p. 660. ISBN 9780415972352.
- "Glasgow Photographic Exhibition". British Journal of Photography: 441. 15 September 1876.
- Pritchard, Baden H. (1882). The Photographic Studios of Europe. London: Piper & Carter. p. 200.
- Stevenson, Sara (1990). Thomas Annan, 1829-1887. Edinburgh: National Galleries of Scotland. pp. 7–8.
- Annan, Thomas Statutory Death 626 A1 0090
- "Close Encounters: Thomas Annan's Glasgow". nationalgalleries.org. National Galleries Scotland.
- "Thomas Annan: Photographer of Glasgow". Retrieved 23 April 2018.