Ferg specialised in scenes that combined classical ruins with everyday peasant life. His work often features Roman ruins, as seen in Romeinse ruïne or Drie herders rustend in een landschap met ruïnes. He used a muted palette to create a specific atmosphere. The figures in his paintings are usually small. This choice provides a sense of scale against the crumbling stone structures. The contrast between grand ancient architecture and humble daily tasks is a defining feature of his style.

Modern collectors value these works for their architectural precision and calm mood. The small scale of the original copper paintings translates well to high-quality prints for domestic spaces. Pieces like Gezin haalt water bij een ruïne offer a window into eighteenth-century tastes for the antique. These prints provide a balanced composition for both traditional and contemporary interiors.