This steel structure in this picture forms a pattern of diagonal lines. The boys climbing up the tube also are leaning on a diagonal. Some have interpreted diagonal lines in an picture to imply energy. Other compositional techniques use horizontal and vertical lines as well. Don’t take “lines” literally. In this picture there are actual lines formed by a steel structure. But a picket fence in a picture would have vertical lines (visually). Often there is a repeating pattern in a picture with horizontal, vertical or diagonal line elements.

See more diagonal line pictures.