This is a group of four stamps from a larger set. Most of the photographs were taken by Lewis Hine, a famous photographer. According to Wikipedia, "Lewis Wickes Hine (September 26, 1874 – November 3, 1940) was an American sociologist and photographer. Hine used his camera as a tool for social reform. His photographs were instrumental in changing the child labor laws in the United States."
More images can be found at http://www.loc.gov/pictures/collection/nclc/.
More industry and technology can be found at See it on a Postcard.