His subjects are barns, one-room schools, courthouses, rural churches, banks, and houses from rural areas and small towns. He works in large format black and white, drawing from more than thirty years as a professional photographer. Harker calls his images little time machines carrying forward to future generations of Iowans the dedication of their forbearers, so people born a century from now will be able to look back in time to what was once glorious and real.