The Thames at Westminster Stairs (1630s) by Claude de Jongh

Halley Docherty (Reddit user halz) has created 15 more stunning images of London by mashing up old paintings and placing them in their modern setting. You can view the original set of images here.

View of London Bridge (1632ish) by Claude de Jongh

Gin Lane (1751) by William Hogarth

Trafalgar Square (1837ish) by James Pollard

Hatchetts - The White Horse Cellar, Piccadilly (1850ish) by James Pollard

Waterloo Place (1886) by Filippo Baratti

North Country Mails at the Peacock Islington (1821)by James Pollard

View of the Strand from the Corner of Villers Street (1830-40) by George Sharf

A Sunset with a View of Nine Elms (1750-65) by Samuel Scott

Newington Turnpike and a View of the Elephant and Castle (1825) by Gideon Yates

Elephant and Castle, Newington (1826) by Samuel Jones

View of Hammersmith Broadway and Queen Street (1831–1838) by James Pollard

A View of Fulham from Putney with Old Fulham Bridge, All Saints Church and the Bridge Toll House (1730ish) by Joseph Nicholls

Old Walton Bridge (1754) by Canaletto

Old Walton Bridge [Detail] (1754) by Canaletto

You can read about the history of each image from the imgur page here.