Londoner and Reddit user shystone superimposed classic paintings of London onto modern images of the city taken from Google Streetview. The result is fascinating, and you can see it here, in an Imgur album compiling the whole set, along with bits of historical information and insights into the area.
This isn't the first effort to mash up historical images with modern ones. The project History Pin uses the same kinds of methods that shystone, but with photographs. You can browse the map, search by place and by time, and add old pictures and the stories behind them. Ever wanted to know what the Willamsburg Bridge in New York looked like in 1909? Or what Cincinnati’s Music Hall looked like in 1888?