Initially intended as an insult, the term Ashcan came to refer to artists at the start of the 20th century who challenged the art establishment and also the Impressionists with works that involved the artists with urban life -- usually the bleak and gritty facets. Early Ashcan artists tended to be Philadelphia Press illustrators (prior to photographic reporting). A New York exhibition of a group called "The Eight" in 1908 prompted critics, repulsed by the vulgarity of subject matter (street urchins, tenements, prostitutes, boxers, etc.), to dub them "The Apostles of Ugliness" and "the revolutionary black gang" because of their dark palattes (Dempsey 79).
The Ashcan innovations "turned a humane gaze on the urban poor, who were either invisible or sentimentalized in academic painting. Their scenes of everyday life made a strong appeal to the 'common man' and gave new vigour to a tradition of artistic protest" (Dempsey 80).
Check out George Bellows' Cliff Dwellers and Steaming Streets, Everett Shinn's Fire on Twenty Fourth Street, Ernest Lawson's Queensborough Bridge (1909), and John Sloan's The City from Greenwich Village (1922).
Dempsey, Amy. Art in the Modern Era: A Guide to Styles, Schools & Movements. NY: Harry N. Abrams Inc., Pub., 2002. 78-80.