While doing research for his PhD dissertation about railroad tramps, he rode freight trains for 20,000 miles (32,000 km) in the western United States.
Harper made extensive use of photo elicitation interviews in his 1987 book, Working Knowledge, a sociological treatment of the rural bricoleur in America.
[5] His 2001 publication, Changing Works, applied the same method to the historical reconstruction of cultural memory.
In 2014, he studied the sociology of public space in the Italian piazza and in the de-industrialized regions of the American Rust Belt.
Harper was co-founder of the International Visual Sociology Association with Leonard M. Henny and others; in 2013 he was elected its president.